gui canvas: draw world overlays too

Code was disabled probably for testing.
driver pigcs: support moveAbs

converted to moveRel for controllers that don't support absolute moves
util polar: small clean up
gui overlay: fix display of point AR after resize

offset computation was not updated. Better do as the rest, always recompute.
util polar: fix cropping

the center of the cropping circle is actually a bit more bellow the bottom of the mirror.
gui canvas: let the overlays now of the resizing before drawing them

if the buffer is resized, we immediately redraw... and then pass the event to the overlays.
It's makes more sense to do the opposite. Probably doesn't affect any code.
driver simcam: new simulated camera

very simple, and able to simulate any kind of image, including RGB.

Should help to simulate the overview camera of the Phenom.

untested.
Merge branch 'master' of vpn.delmic.com:odemis
driver pigcs: fix tests
driver andorcam3: add comment
util polar: spelling fix