Remove progress windows when loading kolab

The Progress bar shown when loading the kolab ressources
for calendar and addressbook opened in a new window because
the main windows is blocked in that period.
On modern desktop computers this usually is over before one
could even read what the window was about and just an annoying
filcker changing the window layout. If it takes longer it was
annyoing because the progress window stole the focus and one was
unable to do something else during that time.

Now a busy cursor is used to indicate that loading is still
in progress.

Fixes:
kolab/issue4859