Blender Git Loki

-some early WIP for strip alignment:

Overall Need:
UI:
-ability to add NlaStrip preblend transform elements using UI
-add, remove, clear
-bone_name from selection, from active
-ability to copy bone targets between strips

UI:
-visualization of traversal bone for general alignment,
similar to motion paths but without the need for an accurate world
transform. It should update as preblend xform changes. Ideally this
path is grabbale and transformable like any other object.
Would require making own transform_convert_stripPreBlendTransform
code... (opportunity to make Python API for it?)

Core algorithm implementation:
-instead of blending strips as their value obtained, we need to
get all raw values. Then apply preblend xform, then we can blend the
whole snapshot. For efficiency, we can allocate the relevant NlaEvalChannels
for bones right after creating NlaEvalData.