Added menu to mark message unread

Fixes #132

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

@@ -697,6 +697,9 @@ public class FragmentMessage extends FragmentEx {
             case R.id.menu_show_headers:
                 onMenuShowHeaders();
                 return true;
+            case R.id.menu_unseen:
+                onMenuUnseen();
+                return true;
             case R.id.menu_answer:
                 onMenuAnswer();
                 return true;
@@ -783,6 +786,40 @@ public class FragmentMessage extends FragmentEx {
         }.load(this, new Bundle());
     }
 
+    private void onMenuUnseen() {
+        Bundle args = new Bundle();
+        args.putLong("id", message.id);
+
+        new SimpleTask<Void>() {
+            @Override
+            protected Void onLoad(Context context, Bundle args) throws Throwable {
+                long id = args.getLong("id");
+
+                DB db = DB.getInstance(context);
+                try {
+                    db.beginTransaction();
+
+                    EntityMessage message = db.message().getMessage(id);
+                    db.message().setMessageUiSeen(message.id, false);
+                    EntityOperation.queue(db, message, EntityOperation.SEEN, true);
+
+                    db.setTransactionSuccessful();
+                } finally {
+                    db.endTransaction();
+                }
+
+                EntityOperation.process(context);
+
+                return null;
+            }
+
+            @Override
+            protected void onLoaded(Bundle args, Void data) {
+                finish();
+            }
+        }.load(this, args);
+    }
+
     private void onMenuAnswer() {
         DB.getInstance(getContext()).answer().liveAnswers().observe(getViewLifecycleOwner(), new Observer<List<EntityAnswer>>() {
             @Override

app/src/main/res/menu/menu_view.xml

@@ -39,6 +39,12 @@
         android:title="@string/title_show_html"
         app:showAsAction="never" />
 
+    <item
+        android:id="@+id/menu_unseen"
+        android:icon="@drawable/baseline_mail_24"
+        android:title="@string/title_unseen"
+        app:showAsAction="never" />
+
     <item
         android:id="@+id/menu_answer"
         android:icon="@drawable/baseline_reply_24"