Add dynamic launcher shortcuts.

Currently the shortcuts are created for the top 3 contacts returned from
Contacts.CONTENT_STREQUENT_URI

Test:
Added unit tests for DynamicShortcuts but currently suppressed because they
require AndroidJUnitRunner
Manual:
* Use N_MR1 device with recent dogfood Nexus launcher installed.
* launch app
* star some contacts if needed
* press home
* long press launcher icon
* verify that starred contacts show in list of shortcuts
* unstar some contacts
* verify that shortcuts change
* pin a shortcut
* remove contact for pinned shortcut
* verify that pinned shortcut is disabled
* pin a shortcut
* change name of contact for pinned shortcut
* verify that name on pinned shortcut changes

Also prevent disambiguation dialog for other home screen shortcuts

Bug 30189449
Bug 31628994
Change-Id: Iace4b1c88b51ba1f7973c6f4ef90002fb92d0784