The S60Manager instantiated the device manager, which then tried
to restore the devices with not all factories being present, resulting
in most saved devices being lost.
That instantiation is now moved to a point in time when all plugins
have been initialized.

Change-Id: I15145bddde89dd6109e092a7b8e03bb92934a29a
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>