ActivityManager: Donot take launcher screenshot.

Currently ActivityManger takes screenshot for all activities
on an activity switch, for maintaining the screenshots in recent
app list. This can be skipped for launcher, as launcher is not
present in the recent app list.

Change-Id: I22f7cda2c63483ab50e0df4428151503892b7d9b
framework:Thread synchronization for UI update

Issue : Framework reboot was observed due to out of sync between
        two threads which inturn causes Null pointer exception
        while updating airplanemode.
Fix : Handled Null pointer exception and the crash is not observed.
CRs-Fixed: 570122

Change-Id: I2e969f6e7726ffcf8648b366ebb54cb2b0afc292
SystemUI: Fix missing top task in recent panel.

If preloadRecentTasksList was not called or was called too
late and RecentsActivty already started and last top activity has
excludeFromRecents flag setted it might be missing
from recent application list.

Change-Id: Idf7153824805ceea9fcaf04ac645b73a5e93a4d9