BSLagBoneController support

[TackYs]

@niftools/blender-niftools-addon-reviewer

Overview

[Overview of the content of the pull request] BSLagBoneControllers are available in the nifformat but not exposed, this is a simple setup to allow for import and export.

Detailed Description

[List of functional updates] The implementation is entirely custom property driven on niftools bone properties, it doesn't cause any actual behavior on the blender side. The behavior of lagbones would be quite similar to 'wiggle' or 'jiggly' bones in blender but those are addons, afaik similar functionality doesn't exist in base blender...

Fixes Known Issues

[Ordered list of issues fixed by this PR] None, new feature

Documentation

[Overview of updates to documentation] I should add some, if you think this PR has some merit. Afaik lagbones are Skyrim only and in LE they work for skeletons and skins, whereas in SSE its skeleton only (caveat; I think this is the case, might be off)

Testing

[Overview of testing required to ensure functionality is correctly implemented] Import/export nif with bslagbones set.

Manual

[Set of steps to manually verify updates are working correctly]

Automated

[List of tests run, updated or added to avoid future regressions]

Additional Information

[Anything else you deem relevant] I've not set up properties for everything, just the ones I think are meaningful, should I? Should this be refactored/ placed somewhere else?