Currently only circle and square, might be easily
extended in the future.
New primitives are creating at cursor location.
This also implied adding 2d cursor to space clip.
Also fix set 2D cursor location which didn't work
in image editor's mask mode since 2.67.
TODO: draw_image_cursor better be moved to some
more generic file, but it's not so much
important for now and might be solved later.
Thanks Campbell for the review!
Snapping operator in action editor for grease pencil and mask wasn't implemented. We could probably re-enabled/fix/cleanup more things in this area (e.g. use a custom poll func for operators not supporting gp/mask, instead of silently doing nothing), but this is for after 2.65 imho).
- image space used wrong notifiers.
- image notifier now checks for mask mode before listening to mask edits.
- mask keyframes now draw in the image space.