Small layout improvement

app/src/main/java/eu/faircode/email/ActivityView.java

@@ -40,7 +40,7 @@ import android.text.TextUtils;
 import android.view.LayoutInflater;
 import android.view.MenuItem;
 import android.view.View;
-import android.widget.ImageView;
+import android.widget.ImageButton;
 import android.widget.ScrollView;
 import android.widget.Toast;
 
@@ -87,11 +87,11 @@ public class ActivityView extends ActivityBilling implements FragmentManager.OnB
     private ActionBarDrawerToggle drawerToggle;
     private ScrollView drawerContainer;
     private RecyclerView rvAccount;
-    private ImageView ivExpanderUnified;
+    private ImageButton ivExpanderUnified;
     private RecyclerView rvUnified;
     private RecyclerView rvFolder;
     private RecyclerView rvMenu;
-    private ImageView ivExpanderExtra;
+    private ImageButton ivExpanderExtra;
     private RecyclerView rvMenuExtra;
     private Group grpUnified;
 

app/src/main/java/eu/faircode/email/AdapterFolder.java

@@ -37,6 +37,7 @@ import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
+import android.widget.ImageButton;
 import android.widget.ImageView;
 import android.widget.TextView;
 
@@ -95,7 +96,7 @@ public class AdapterFolder extends RecyclerView.Adapter<AdapterFolder.ViewHolder
         private ImageView ivReadOnly;
 
         private View vwLevel;
-        private ImageView ivExpander;
+        private ImageButton ivExpander;
 
         private ImageView ivUnified;
         private ImageView ivSubscribed;

app/src/main/java/eu/faircode/email/AdapterMessage.java

@@ -232,7 +232,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
         private View view;
 
         private View vwColor;
-        private ImageView ivExpander;
+        private ImageButton ivExpander;
         private ImageView ivFlagged;
         private ImageView ivAvatar;
         private TextView tvFrom;
@@ -256,7 +256,7 @@ public class AdapterMessage extends RecyclerView.Adapter<AdapterMessage.ViewHold
 
         private View vsBody;
 
-        private ImageView ivExpanderAddress;
+        private ImageButton ivExpanderAddress;
 
         private ImageButton ibSearchContact;
         private ImageButton ibNotifyContact;

app/src/main/res/layout/include_message_addresses.xml

@@ -13,7 +13,7 @@
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent" />
 
-    <ImageView
+    <ImageButton
         android:id="@+id/ivExpanderAddress"
         android:layout_width="0dp"
         android:layout_height="24dp"

app/src/main/res/layout/include_message_compact.xml

@@ -22,7 +22,7 @@
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent" />
 
-    <ImageView
+    <ImageButton
         android:id="@+id/ivExpander"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"

app/src/main/res/layout/include_message_normal.xml

@@ -20,7 +20,7 @@
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent" />
 
-    <ImageView
+    <ImageButton
         android:id="@+id/ivExpander"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"

app/src/main/res/layout/include_nav.xml

@@ -20,10 +20,11 @@
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toBottomOf="@id/rvAccount" />
 
-    <ImageView
+    <ImageButton
         android:id="@+id/ivExpanderUnified"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
+        android:background="?android:attr/selectableItemBackground"
         android:contentDescription="@string/title_legend_expander"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toBottomOf="@id/vSeparatorAccount"
@@ -77,10 +78,11 @@
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toBottomOf="@id/rvMenu" />
 
-    <ImageView
+    <ImageButton
         android:id="@+id/ivExpanderExtra"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
+        android:background="?android:attr/selectableItemBackground"
         android:contentDescription="@string/title_legend_expander"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toBottomOf="@id/vSeparatorMenu"

app/src/main/res/layout/item_folder.xml

@@ -53,7 +53,7 @@
                 app:layout_constraintStart_toEndOf="@id/ivState"
                 app:layout_constraintTop_toTopOf="parent" />
 
-            <ImageView
+            <ImageButton
                 android:id="@+id/ivExpander"
                 android:layout_width="wrap_content"
                 android:layout_height="0dp"

app/src/main/res/layout/item_folder_select.xml

@@ -19,11 +19,12 @@
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toTopOf="parent" />
 
-        <ImageView
+        <ImageButton
             android:id="@+id/ivExpander"
             android:layout_width="36dp"
             android:layout_height="0dp"
             android:layout_gravity="center_vertical|center_horizontal"
+            android:background="?android:attr/selectableItemBackground"
             android:contentDescription="@string/title_legend_expander"
             android:padding="6dp"
             app:layout_constraintDimensionRatio="1:1"

app/src/main/res/layout/item_folder_unselectable.xml

@@ -42,7 +42,7 @@
                 app:layout_constraintStart_toEndOf="@id/ivState"
                 app:layout_constraintTop_toTopOf="parent" />
 
-            <ImageView
+            <ImageButton
                 android:id="@+id/ivExpander"
                 android:layout_width="wrap_content"
                 android:layout_height="0dp"