No activity while uninstalling unless needed

In many cases uninstalling does not require any acticity. In this case,
just show a notification instead of a problematic translucent activity.

Note: In a future change this will also allow uninstallation for all
users. This might need API changes though.

Test: Simulated all error and success scenarios
Change-Id: Iaa655fecc981b7274b995608f6e9b428f84a8d7d