Add UI for redefining existing "traditional" OpenSim frames as point-based frames

[adamkewley]

• Add a context menu to the model editor such that when a user right-clicks a "normal" OpenSim frame, there is something like Warping > Redefine Frame from Landmarks
• Clicking this then searches for associated landmarks for the mesh (e.g. at Landmarks/Mesh.csv) and loads them
• Then the user uses those landmarks to define a frame
• But the UI also shows the previous position of the frame, so that the user can ensure their new definition aligns well-enough with it (because the user probably doesn't want to break an existing model when doing this)
• The frame definition should be saved to framedefs.toml next to the model (warping workflow) - this file should be checked+reloaded whenever the user tries to use Redefine Frame from Landmarks in the future, and it acts as an associative store for frame definitions that is backward-compatible with OpenSim4