Print spooler UI polish and bug fixes.

1. Added an empty state for pages that are being rendered.

2. Fixed a NPA on a binder thread when destoroying the
   remote print adapter.

3. Fixed a rare crash when the print activity gets an
   activity class callback while initializing.

4. Changed the preview pages on phone in land to four.

5. Fixed a flicker from a list of pages to an empty state
   and then back to the list of pages.

bug:15704969
bug:16966145

Change-Id: I0eea2f30a102d8fefcbf90187fa6d8612fb19434

Conflicts:
	packages/PrintSpooler/src/com/android/printspooler/widget/PageContentView.java