Add Volume panel

Volume panel hosts each volume stream, including:
- Media volume
- Call Volume
- Ring volume
- Alarm volume

Change-Id: I1801d10d2304c57615e9499386c638c74ffcd7c3
Screenshot: https://screenshot.googleplex.com/m764j65ECto
Bug: 117804161
Test: Manual app
Test: robolectric

src/com/android/settings/panel/SettingsPanelActivity.java

@@ -54,6 +54,9 @@ public class SettingsPanelActivity extends FragmentActivity {
     // TODO (b/117804442) move to framework
     public static final String PANEL_TYPE_WIFI = "wifi_panel";
 
+    // TODO (b/117804442) move to framework
+    public static final String PANEL_TYPE_VOLUME = "volume_panel";
+
     @Override
     protected void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);