Add plugin controls to tuner

Allow plugins to be manually turned off from within the tuner. This
screen only shows itself if at some point in time a plugin has been
active on this device.  Plugins can also serface settings there by
receiving the com.android.systemui.action.PLUGIN_SETTINGS action.

Test: Manual
Change-Id: Ifb043c85e383fc072c6445ae322293a6401a6f2c
diff --git a/packages/SystemUI/plugin/ExamplePlugin/AndroidManifest.xml b/packages/SystemUI/plugin/ExamplePlugin/AndroidManifest.xml
index bd2c71c..ff89bbc 100644
--- a/packages/SystemUI/plugin/ExamplePlugin/AndroidManifest.xml
+++ b/packages/SystemUI/plugin/ExamplePlugin/AndroidManifest.xml
@@ -21,7 +21,15 @@
     <uses-permission android:name="com.android.systemui.permission.PLUGIN" />
 
     <application>
-        <service android:name=".SampleOverlayPlugin">
+        <activity android:name=".PluginSettings"
+            android:label="@string/plugin_label">
+            <intent-filter>
+                <action android:name="com.android.systemui.action.PLUGIN_SETTINGS" />
+            </intent-filter>
+        </activity>
+
+        <service android:name=".SampleOverlayPlugin"
+            android:label="@string/plugin_label">
             <intent-filter>
                 <action android:name="com.android.systemui.action.PLUGIN_OVERLAY" />
             </intent-filter>