Added ability to scan library in SettingsFragment

app/src/main/res/xml/global_preferences.xml

@@ -28,6 +28,10 @@
             app:title="@string/theme_selection"
             app:useSimpleSummaryProvider="true" />
 
+        <Preference
+            android:key="scan_library"
+            android:title="Scan library" />
+
         <Preference
             android:key="logout"
             android:title="Log out" />