TARGIT upgrade should include functionality to delete old versions of clients

When you upgrade your TARGIT solution, the clients are upgraded as well, however there is no bulit-in funcitonality to clean up old versions of TARGIT Clients.

This will accumulate disk space over time and in any case the old clients are redundant.

(Since a TARGIT end-user potentially can access multiple TARGIT solutions running on different versions, the deleting shouldn't be automatic - but supported as an option in the client installer.