Keyguard: Allow applications to customize left-corner widget

Adds ability for trusted applications to set the application widget and
action in the lower left corner of the Keyguard.  Its behavior is
modeled against the on-screen camera widget most commonly found on the
lower right corner of the Keyguard.

Three intents are defined: one to set the widget, one to clear the
widget, and one to notify when the widget is activated.

Applications calling this intent must have this permission:
android.permission.SET_KEYGUARD_APPLICATION_WIDGET.

Change-Id: I8c5b11fd1cc1888c710bf3736e3c28d77fc57e37

Conflicts:
	core/java/com/android/internal/policy/IKeyguardService.aidl
	core/res/AndroidManifest.xml
	packages/Keyguard/src/com/android/keyguard/KeyguardService.java
	packages/Keyguard/src/com/android/keyguard/KeyguardViewManager.java
	packages/Keyguard/src/com/android/keyguard/KeyguardViewMediator.java
	packages/SystemUI/AndroidManifest.xml
	packages/SystemUI/res/layout/navigation_bar.xml
	packages/SystemUI/src/com/android/systemui/statusbar/phone/KeyguardTouchDelegate.java
	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarTransitions.java
	packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarView.java
	policy/src/com/android/internal/policy/impl/keyguard/KeyguardServiceWrapper.java