#786 Needbased Backup functionality broken

[Stefan Rossbach]

Activities are now executed async (old behavior = sync) that is now causing the backup feature to fail.

Reason: The "Feature" pops up a GUI Dialog out of the logic code. While this dialog is active every queued
activity gets executed and so saving the editor with dirty content and creating a backup of these contents.

The primary failure is that the needbased (File)activity has already been processed by the SarosSession and so
the file is marked as shared and thats way further Jupiter Activities are able to modifiy the file before it is even
backuped.

[Stefan Rossbach]

Activities are now executed once again sync. Marked as remind to not produce the same defect again.