Blender Git Loki

Mask points now could be parented to the plane track

MaskParent structure was extended by:
- type, which indicates whether it's a parent to point
or plane track. Types might be extended further.

- Original corners, which are used to obtain homography
used to deform point's coordinate.

Homoraphy is detecting between original corners position
(corners at the parenting time) and current plne corners,
and the it's being applied on mask point coordinate.

Some tricks with switching between mask and clip coords
is needed, but it's all pretty much straightforward in
the code.

Parenting happens on spline point level, not spline one.
This fits existing design, and it's not so big difference
for artist.

Parenting operator (Ctrl-P) might for sure be used to
parent points to the active plane track.

Additional change: added visualization of plane corners
orientation. Corner which corresponds to left bottom
image corner now has got two axis: red which corresponds
to X axis, and green one for Y axis. This way it's
easier to orient corners on the footage.