Added support for async inflation of RemoteViews

When enabled, the View inflation as well as some of the drawable
loading is done on the background thread.
It also assumes that all the views support inflation on the
background thread, which is true for the default views
supported by the platform

For ViewGroup opetations, it maintains a virtual view tree which
is used for findViewById. The final operations are applied on
the UI thread in the end.

Change-Id: Ib3ce55182ec04a344f2b2513981ee03afc8fa2e8