Blender 2.9 Migration

Problem: We need a good strategy to migrate to blender 2.9 without blowing up our checkout (2.7 needs to stay working while we are migrating) and also our repo. Solution: We'll (sorta) follow Subversion's migration strategy:

1. the two main folders to migrate are lib/ and scenes/ in the main project folder.
2. create branches/blender29/ in main tube/ folder
3. create lib/ and scenes/ in the blender29/ folder
4. commit these to Subversion
5. copy or move (windows) or symlink (linux) lib/maps and lib/maps_low if needed/
6. replicate the rest of the folder structures under lib/ and scenes/ (excluding the existing *28/ ) folders and commit these to subversion
7. Create a new addon that is a combination of the old sparkleshart and migrate28, that uses svn copy to duplicate the files, and then migration heuristics to change those files.
8. Manually check, copying/ changing if needed
9. Commit new files

Much later:

• SVN delete the old lib/ and scenes/ file
• SVN rename the folders to switch branches/blender29/ to main/