Fix Custom Resolver Theming

Theming wasn't working with a custom resolver and the culprit was the
fact that the PackageManagerService was overriding the theme with no
theme. This fix looks through the package and finds the correct theme
for the activity.

Change-Id: I6b253a236ae2a868acb0374384ba1ae58efa5b5e
(cherry picked from commit 86092491)