Add copyright to CMakeLists.txt
Update Graphene and Window classes

Rename Graphene class to Engine, equally named namespace and class emerged
some problems in example application code.
Split mouse handler into two (motion + buttons), add a separate hanled for
'idle' event (message queue drained).
Add default handler for 'quit' event.
Add usefull methods like getKeyboardState() to Window class (see diff).
Update example application

Update code for recent library changes.
Ass FPS-alike camera movement.