Reenable fixed-placed pip

Hi

after we've used this patched version of DVSwitch successfully at the FOSSGIS 2014 I'd ask for comments on integrating the changes into the voc-mainline version.

This patch re-enables PIP (Picture-in-Picture) for DVSwitch in a more fool-proof fashion:
 - The PIP-Placement is fixed, it can be set via commanline if required.
 - The only control available to the operator is toggeling the PIP on and of (using the 'p'-key).
 - The PIP is automatically disabled, when it would show the same content as the main video

Switching the PIP-Content is done by pressing Ctrl+[1-9], which is a shortcut in the range of Ctrl-i (enable audio toggle) - usually not pressed by the operator.

Regards,
Peter