Blender Git Loki

T45687: Rework the Export/Import of Animations

This started with a fix for an animated Object Hierarchy. Then i decided to cleanup and optimize a bit. But at the end this has become a more or less full rewrite of the Animation Exporter. All of this happened in a separate local branch and i have retained all my local commits to better see what i have done.

Brief description:

* I fixed a few issues with exporting keyframed animations of object hierarchies where the objects have parent inverse matrices which differ from the Identity matrix.
* I added the option to export sampled animations with a user defined sampling rate (new user interface option)
* I briefly tested Object Animations and Rig Animations.

What is still needed:

* Cleanup the code
* Optimize the user interface
* Do the Documentation

Reviewers: mont29

Reviewed By: mont29

Differential Revision: https://developer.blender.org/D3070