Do not allow duplicate shortcuts when ALL_APPS is disabled.

When DISABLE_ALL_APPS is true, we want to have only one shortcut for each activityexposed via the Application's manifest.
We ignore INSTALL_SHORTCUT broadcasts which have launch intents with ACTION_MAIN and CATEGORY_LAUNCHER.
Applications can still create shortcuts pointing to an already exposed component if they provide data or extras in the intent.

Change-Id: I0b05283ea6c522d197e0262c2997f7298e08740b