Blender Git Loki

Couple of changes to keying node:

- Switch from gaussian-bokeh blur to mean-value which is much faster
and from matte's quality behaves not worse than gaussian-bokeh.
- Added Edge matte output so areas where black/white clipping happens
could be easily controlled.

Currently not sure if it's possible than operation returns two
buffers, so now implemented as separate clipping operation call
with specific options.

- Changed logic of detecting edges - check if most pixels within
kernel are different fits some tolerance interval.

- Added two extra options which controls how edges are detecting:

* Edge Kernel Radius defines radius of kernel within pixel's value
is checking.
* Edge Kernel Tolerance defines maximal difference between value
of current pixel and it's neigbours which are trated as belng to
the same plane )background of foreground)

Unfortunately, value for this two sliders for existing files shall
be tweaked manually. Default values are 3 for radius and 0.1 for
tolerance.