SystemUI: fix wrong statusbar background.

If we turned off screen while some panel was visible than
background of PhoneStatusBarView will not be updated because we receiving single
panelExpansionChanged call and after super.panelExpansionChanged mFadingPanel
will be null (onAllPanelsCollapsed cause this).

Allow updating background when mFadingPanel is null.

Change-Id: Ib123f27500790c1b7ec787b7e433372629daa08d
Revert "Keyguard: fix statusbar lags when default widget shown."

This reverts commit eda617bd43cd9365f5dd2c887a5cd350763e8a5f.
Keyguard: fix statusbar lags when default widget shown.

When statusbar became expanded KeyguardStatusView receives
onKeyguardVisibilityChanged callback and refreshes ClockView.
Because it receives more than one call and every time it reads
new values from resources it cause lags in opening statusbar panel.

Replace this code with BroadcastReceiver and ContentObserver to
refresh it only in case something was changed.

Change-Id: If0dbc1db059536806852661931cb2e6436f2acf4
[WIP] Multi-window

This is a big work in progress, which currently has some bugs,
but begins to look okay. NO BUG REPORT, NO CODE CLEANUP COMMENTS

You can already multitask a little bit, by using the
app switcher and long-pressing an icon, then select "Add to
Split View".
Last window touched gets the key focus.

Code is very ugly, I know. Don't merge it, don't use it
for now. Unless you want to make your code ugly.

Enjoy :)

Change-Id: I4a03a84539fd3ac1273f0d3503fe8fafcd16be26

Conflicts:
	core/java/android/app/Activity.java
	core/java/android/inputmethodservice/InputMethodService.java
	core/java/android/view/IWindowManager.aidl
	packages/SystemUI/res/values/custom_strings.xml
	packages/SystemUI/src/com/android/systemui/recent/RecentsPanelView.java
	services/java/com/android/server/am/ActivityStack.java
	services/java/com/android/server/wm/WindowManagerService.java