Fix scrollbars

Fixes #5487
Closes #5671

// FREEBIE

res/layout/contact_selection_list_fragment.xml

@@ -12,7 +12,8 @@
         <android.support.v7.widget.RecyclerView
             android:id="@+id/recycler_view"
             android:layout_width="match_parent"
-            android:layout_height="match_parent" />
+            android:layout_height="match_parent"
+            android:scrollbars="vertical" />
 
         <TextView android:id="@android:id/empty"
             android:layout_width="match_parent"

res/layout/media_overview_activity.xml

@@ -9,7 +9,8 @@
     <android.support.v7.widget.RecyclerView
             android:id="@+id/media_grid"
             android:layout_width="match_parent"
-            android:layout_height="match_parent" />
+            android:layout_height="match_parent"
+            android:scrollbars="vertical" />
 
     <TextView android:id="@+id/no_images"
               android:layout_width="match_parent"

src/org/thoughtcrime/securesms/ContactSelectionListFragment.java

@@ -162,7 +162,9 @@ public class ContactSelectionListFragment extends    Fragment
   public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
     ((CursorRecyclerViewAdapter) recyclerView.getAdapter()).changeCursor(data);
     emptyText.setText(R.string.contact_selection_group_activity__no_contacts);
-    if (recyclerView.getAdapter().getItemCount() > 20) {
+    boolean useFastScroller = (recyclerView.getAdapter().getItemCount() > 20);
+    recyclerView.setVerticalScrollBarEnabled(!useFastScroller);
+    if (useFastScroller) {
       fastScroller.setVisibility(View.VISIBLE);
       fastScroller.setRecyclerView(recyclerView);
     }