Clarify licensing terms for models

[ugermann]

Catalog-entry.yml has licensing info at least for some models, model-info.json appears not to have it.

1. Is there any particular reason that some models are CC-BY-SA-NC (e.g., bg<->en)? I'd prefer CC-BY-SA in most cases, unless there is a particular reason to make them *-NC. If there is a reason (e.g., corpora used), this should be documented.
2. If catalog-entry.yml is removed, licensing terms should be documented elsewhere (e.g. in model-info.json).

On a marginal note: As a rule of thumb I prefer yaml over json, because the former allows comments whereas the latter, to the best of my knowledge, doesn't.

[ugermann]

See also #49.