Improve configuration of default preferred apps.

The file that defines default preferred apps is now more
robust.  It is no longer a raw dump of the package
manager settings, but instead a more general list of a
target activity and filter.  When reading it, the remaining
information (match value, set of potential matches) is
determined dynamically.

Change-Id: I0edc6e0d2ed3dd2a6e2238992f18f7fc1f51d8d4