Add support for Blender 5

[hubbardp]

Several parts of neuVid use action.fcurves, which is no longer supported as of Blender 5:

https://developer.blender.org/docs/release_notes/5.0/python_api/#animation-rigging

"Instead of action.fcurves and action.groups, access those properties on the channelbag. Each slot of an Action can have a channelbag. You can use the convenience functions in bpy_extras.anim_utils to get one, or to ensure one exists."