Add option to disable subtasks

Subtasks are disabled by default

app/src/main/java/org/tasks/preferences/BasicPreferences.java

@@ -113,7 +113,14 @@ public class BasicPreferences extends InjectingPreferenceActivity
         R.string.p_linkify_task_list,
         R.string.p_show_list_indicators);
 
-    findPreference(getString(R.string.customize_edit_screen))
+    findPreference(R.string.p_show_subtasks)
+        .setOnPreferenceChangeListener((preference, newValue) -> {
+          forceRestart();
+          localBroadcastManager.broadcastRefresh();
+          return true;
+        });
+
+    findPreference(R.string.customize_edit_screen)
         .setOnPreferenceClickListener(
             preference -> {
               startActivityForResult(

app/src/main/java/org/tasks/preferences/Preferences.java

@@ -5,6 +5,7 @@ import static com.google.common.collect.Iterables.filter;
 import static com.google.common.collect.Iterables.transform;
 import static com.google.common.collect.Sets.newHashSet;
 import static com.todoroo.andlib.utility.AndroidUtilities.atLeastKitKat;
+import static com.todoroo.andlib.utility.AndroidUtilities.atLeastLollipop;
 import static java.util.Collections.emptySet;
 
 import android.content.ContentResolver;
@@ -527,4 +528,8 @@ public class Preferences {
   public int getDefaultPriority() {
     return getIntegerFromString(R.string.p_default_importance_key, Priority.LOW);
   }
+
+  public boolean showSubtasks() {
+    return atLeastLollipop() && getBoolean(R.string.p_show_subtasks, false);
+  }
 }

app/src/main/java/org/tasks/ui/TaskListViewModel.java

@@ -109,6 +109,7 @@ public class TaskListViewModel extends ViewModel {
 
     if (filter.supportSubtasks()
         && (includeGoogleTaskSubtasks || includeCaldavSubtasks)
+        && preferences.showSubtasks()
         && !(preferences.isManualSort() && filter.supportsManualSort())) {
       String tagQuery =
           Query.select(field("group_concat(distinct(tag_uid))"))

app/src/main/res/values/keys.xml

@@ -308,4 +308,5 @@
   <string name="google_tasks_position_hack">Custom order synchronization fix</string>
   <string name="google_tasks_position_hack_summary">Always perform a full synchronization to workaround https://issuetracker.google.com/issues/132432317</string>
   <string name="subscription_help_url">https://tasks.org/subscribe</string>
+  <string name="p_show_subtasks">show_subtasks</string>
 </resources>

app/src/main/res/values/strings.xml

@@ -560,4 +560,6 @@ File %1$s contained %2$s.\n\n
   <string name="subtasks_enable_synchronization">Enable synchronization to add subtasks</string>
   <string name="subtasks_multilevel_google_task">Multi-level subtasks not supported by Google Tasks</string>
   <string name="enter_title_hint">Enter title</string>
+  <string name="show_subtasks">Show subtasks</string>
+  <string name="show_subtasks_summary">Displaying subtasks will degrade app performance</string>
 </resources>

app/src/main/res/xml/preferences.xml

@@ -38,6 +38,12 @@
       android:key="@string/p_rowPadding"
       android:title="@string/row_spacing"/>
 
+    <CheckBoxPreference
+      android:defaultValue="false"
+      android:key="@string/p_show_subtasks"
+      android:title="@string/show_subtasks"
+      android:summary="@string/show_subtasks_summary" />
+
     <com.todoroo.astrid.ui.MultilineCheckboxPreference
       android:defaultValue="false"
       android:key="@string/p_fullTaskTitle"