ShortcutManager: finishing touches

- Change back the throttling quota to 10 calls / day
- Foreground apps are no longer throttled, and when an app comes to
foreground the call counter will be reset.
- When the system locale changes, reset throttling for all packages
for all users.
  See LocalService.onSystemLocaleChangedNoLock() for how it's performed.
  Because the reset must happen before any other apps have a chance to
  publish shortcuts, the logic is not straightforward.

- Added an internal API to reset the throttling upon inline-reply
from a notification.

- Stop supporting icons from "content:" URIs
- Improved javadoc on several APIs.

Also internal refactor needed to this:
- ShortcutUser.getAllPackages()/getAllLaunchers() are no longer
accessible to outer code to prevent accidentally adding/removing the
content.  Outer code should use forAllPackages() / forAllLaunchers().

Bug 27923857

Change-Id: I002511193d1d33718163bb1dabe77610bde58198