Implemented per window keyboard modifyer masks

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Added special key codes for shortcuts

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Added clipboard integration to edit box widget

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>