With the change that the activated signal switches to the current
session the manager becomes unusable e.g. in Linux/KDE with a single
click policy. This is because you can't select a session by mouse any
more in order to use one of the delete/rename/etc buttons.

Change-Id: I4e81ee21f37fba0b4f456e02e9ce2e9da14c5a88
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>