Reader snackbar dismissible (#4190)

* Make Reading Mode Snackbar dismissible

* Change reader FrameLayout to CoordinatorLayout

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

@@ -1,4 +1,4 @@
-<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
@@ -124,4 +124,4 @@
         android:layout_height="match_parent"
         android:visibility="gone" />
 
-</FrameLayout>
+</androidx.coordinatorlayout.widget.CoordinatorLayout>