Blender Git Loki

fix T59743: Collada exporter: Add option for exporting flat curves

The Collada exporter suppresses the export of flat animation curves
to optimize the animation (in fact to make the exported file smaller).

But sometimes it is important to also have the flat curves exported
because they may be needed to define an initial transformation to
a fixed location - like translating the weapon from the ground floor
to the back of the model in the report.

I added a new option "all keyed curves" which is disabled by default
but when enabled it also exports flat curves.

feedback is very welcome