Added RNA access to mask spline's points.

Straightforward patch, point tructure was already defined,
was just matter of defining RNA collection property for
mask spline.

Available via: mask.layers[0].splines[0].points

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56761 954f8c5b-7b00-dc11-b283-0030488c597c