Blender Git Loki

Python API: Expose CurveMapping Reset View function

The Python API for the curve mapping widget offers the `update`
function, but no way to reset the view to the clipping rectangle.

This commit adds a blenkernel function for this operation,
and exposes it to the CurvMapping RNA API. This allows addons
to display a more user-friendly view of the data in this widget.

Differential Revision: https://developer.blender.org/D10561