transducer transform matrix should come with dims

[ebrahimebrahim]

In the database format / data model, the matrix for transforming a Transducer should come with "dims" just like a Point does (e.g. dims=['L','P','S']).

(Here we are talking about the transducer transform matrix that is saved to a session.json, not the (typically identity) matrix that is saved in the transducer definition)

[ebrahimebrahim]

Alternative solution to this: make units and dims just be a property of Session.
From @peterhollender:

I'm working on a proposal for a new Session json format. Is it really useful to store the dims and units separately with the targets, markers (which we may be able to drop) and transducer matrix? I kind of feel like they should all be the same, and just be a property of the session, if they are stored at all. We could easily just decide that sessions are LPS or RAS and mm, and rescale anything that isn't in those coordinates on saving.