Remove beta notification for data binding and add a few docs.
Remove beta notification for data binding and add a few docs.

Removed the beta warning for data binding.
Added information about renamed attributes.
Added information about context variable.

Change-Id: I7052416d8329a0cb812819017087e4e62d81e0c4

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base