Icon API tuneups:

- Reorder parameters to loadDrawableAsync()
- New version of createWithResource that takes a package
  name instead of a Resources
- Add loadDrawableAsUser() for INTERACT_ACROSS_USERS clients
  like SystemUI
- Docs cleanups

Bug: 21089268
Bug: 21031774
Change-Id: I465d2b865e35e12094b564f994e59d55e522f65a