Add ability to open equalizer from SettingsFragment

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

@@ -28,6 +28,11 @@
             app:title="@string/theme_selection"
             app:useSimpleSummaryProvider="true" />
 
+        <Preference
+            android:key="equalizer"
+            android:title="Equalizer"
+            app:summary="Adjust audio settings" />
+
         <Preference
             android:key="scan_library"
             android:title="Scan library" />