Refactoring for better extendability

- Exposing members of PhoneStatusBar, StatusBarKeyguardViewManager and
  KeyguardBouncer to sub class;
- Add a configuable SystemUIFactory as class factory for components;
- Add logoutCurrentUser and switchToByUserId to UserSwitcherController;

BUG:22407003
Change-Id: I3902baf3c721d89217b27a6310c4202a198cb209
diff --git a/packages/SystemUI/proguard.flags b/packages/SystemUI/proguard.flags
index bc18221..2ea8c9c 100644
--- a/packages/SystemUI/proguard.flags
+++ b/packages/SystemUI/proguard.flags
@@ -13,6 +13,7 @@
 -keep class com.android.systemui.statusbar.car.CarStatusBar
 -keep class com.android.systemui.statusbar.phone.PhoneStatusBar
 -keep class com.android.systemui.statusbar.tv.TvStatusBar
+-keep class com.android.systemui.SystemUIFactory
 
 -keepclassmembers class ** {
     public void onBusEvent(**);