fb: fix possible NPE on back button transition

Change-Id: Ia6e30a9d94f292e7616b846f159b61fed9f502cc
fb: slightly adjust navigationring background drawable size

for custom icons to fit the system icons

Change-Id: I068cd0a463484f0f1b3ed0f210701290be364b7a
fb: navigationbar use always slimactions and add contentdescription

No need to use the AOSP implementation at all...we can send all actions
over SlimActions....so remove AOSP implementation and clean up

As well add contentdescription for accessibility events like talkback
for ppl who are not able to see. Gives the user all information back
needed.

Change-Id: I8f82f1139f1248d9cf8e762d6669bb75ae4e205f
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