Initial fcurve simplification code.

Notes:
* This is own coocking, since it seems hard to find papers on simplifying already existing bezier curves,
and we do not really need the 'generic' least-square fitting of bezier in a set of points, here.
* It takes advantage of specificities of FCurves (e.g. only difference that matters here is Y value at same X frame,
no vertical overlapping, etc.).
* It gives reasonably good results, but could most likely be enhanced quite a bit still.
* Only 'hooked' to bake action operator right now (needs more work to add it to graph editor too).
* Ultimately should probably be redone in C. Would keep it in Python until we have a real good
cleanup behavior though, much easier to experiment in later language.