Added 'position' signal which is emitted to inform a change of position
with the current SmartBin.
* pitivi/ui/complextimeline.py:
* pitivi/ui/mainwindow.py:
* pitivi/ui/timeline.py:
* pitivi/ui/viewer.py:
Switch to use playground's 'position' signal in Viewer and
ComplexTimeline.
This should fix several issues:
_ Position checking not being in ui-independent part,
_ Position updating not starting,
_ Position checking done during critical parts (state change).


git-svn-id: svn+ssh://svn.gnome.org/svn/pitivi/trunk@777 d3729300-e425-0410-8a4c-d956edccc248