Commit of basic architecture. Sorry, nothing fun to play with yet. Added two events: MOUSEDRAG and MOUSEDROP. MOUSEDRAG is sent when left-mouse clicking and then moving the cursor and every time the cursor is moved until the user releases the mouse button, thus generating a MOUSEDROP. Also added two dummy drag operators in view3d and outliner (place holders for now). Brecht and Ton: feel free to check/edit especially the event system code. I'm not sure that's the right way to do it. Also, I'm getting some mem leaks which I suspect are caused by my code.