Polish of the ActivityChooserView and ShareActionProvider.

1. Addressed the UX comments: ActivityChooserView's default selection
   popup no longer shows a message, rather hightlights the default
   action which now it displays. Alignemnt of the UI.

2. The ShareActionProvider shows a sub-menu if the host item goes
   on the overflow menu.

3. Now the heade layout of the activity chooser view is not needed hence
   dropped and the item and footer ones are merged.

Change-Id: I0b3de623e4c0a805be9ed73a8541e66b8c00e2d2