Use dedicated UI executor

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

@@ -337,7 +337,7 @@ public class EditTextCompose extends FixedEditText {
                         if (snippet.id.equals(id)) {
                             String html = snippet.getHtml(context, to);
 
-                            Helper.getParallelExecutor().submit(new Runnable() {
+                            Helper.getUIExecutor().submit(new Runnable() {
                                 @Override
                                 public void run() {
                                     try {
@@ -384,7 +384,7 @@ public class EditTextCompose extends FixedEditText {
             });
 
             DB db = DB.getInstance(context);
-            Helper.getParallelExecutor().submit(new Runnable() {
+            Helper.getUIExecutor().submit(new Runnable() {
                 @Override
                 public void run() {
                     try {
@@ -493,7 +493,7 @@ public class EditTextCompose extends FixedEditText {
                 } else
                     html = h;
 
-                Helper.getParallelExecutor().submit(new Runnable() {
+                Helper.getUIExecutor().submit(new Runnable() {
                     @Override
                     public void run() {
                         try {

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

@@ -336,7 +336,7 @@ public class EditTextMultiAutoComplete extends AppCompatMultiAutoCompleteTextVie
                                     Integer has = encryption.get(email);
                                     if (has == null) {
                                         final List<Address> recipient = Arrays.asList(new Address[]{parsed[0]});
-                                        Helper.getParallelExecutor().submit(new Runnable() {
+                                        Helper.getUIExecutor().submit(new Runnable() {
                                             @Override
                                             public void run() {
                                                 try {

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

@@ -10114,7 +10114,7 @@ public class FragmentMessages extends FragmentBase
             return;
 
         DB db = DB.getInstance(context);
-        Helper.getParallelExecutor().execute(new Runnable() {
+        Helper.getUIExecutor().execute(new Runnable() {
             @Override
             public void run() {
                 try {

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

@@ -813,7 +813,7 @@ public class FragmentOptionsNotifications extends FragmentBase implements Shared
                 ComponentName.createRelative(context, cls.getName()),
                 context.getString(title),
                 Icon.createWithResource(context, icon),
-                Helper.getParallelExecutor(),
+                Helper.getUIExecutor(),
                 new Consumer<Integer>() {
                     @Override
                     public void accept(Integer result) {

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

@@ -247,6 +247,7 @@ public class Helper {
 
     private static ExecutorService sSerialExecutor = null;
     private static ExecutorService sParallelExecutor = null;
+    private static ExecutorService sUIExecutor = null;
     private static ExecutorService sMediaExecutor = null;
     private static ExecutorService sDownloadExecutor = null;
 
@@ -265,6 +266,12 @@ public class Helper {
         return sParallelExecutor;
     }
 
+    static ExecutorService getUIExecutor() {
+        if (sUIExecutor == null)
+            sUIExecutor = getBackgroundExecutor(0, 0, 3, "UI");
+        return sUIExecutor;
+    }
+
     static ExecutorService getMediaTaskExecutor() {
         if (sMediaExecutor == null)
             sMediaExecutor = getBackgroundExecutor(0, 1, 3, "media");
@@ -2762,7 +2769,7 @@ public class Helper {
                             ? R.string.title_setup_biometrics_disable
                             : R.string.title_setup_biometrics_enable));
 
-                    final BiometricPrompt prompt = new BiometricPrompt(activity, Helper.getParallelExecutor(),
+                    final BiometricPrompt prompt = new BiometricPrompt(activity, Helper.getUIExecutor(),
                             new BiometricPrompt.AuthenticationCallback() {
                                 private int fails = 0;