Misc cleanup

- Migrate sources filter screen to full compose
- Use standard "OK"/"Cancel" actions for delete category dialog
- Abstract some AppBar logic
- Remove some dead code
- Group related strings

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

@@ -24,7 +24,6 @@
             android:layout_height="95dp"
             android:layout_marginStart="12dp"
             android:layout_marginTop="12dp"
-            android:contentDescription="@string/description_cover"
             android:scaleType="centerCrop"
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toTopOf="parent"