generateTarget() will always find a unique target
fix add user to group to work with grouped shares
fix unit tests
mark exclude list as deprecated. It neither used by the files app nor by the
calendar or contacts app. It doesn't make sense to build a exclude list by the
share API, the apps knows best which are valid targets.
only add a new row if it isn't a unique share, otherwise update the existing row
clear share table after each test run