[Feature]: Enhance TermSet

[rly]

What would you like to see added to HDMF?

See https://github.com/hdmf-dev/hdmf/pull/880#pullrequestreview-1517181868

• Moving ExternalResources, ExternalResourceMangager, TermSet etc. codes into a separate module (folder) for external_resources
• Add TermSet._repr_html_ function similar to #883 for to be able to render term sets nicely in the docs and Jupyter notebooks
• Add read-only properties to TermSet for “name”, “version”, and “prefixes” (which are probably just shortcuts for lookups in TermSet.view)

Is your feature request related to a problem?

No response

What solution would you like?

See above

Do you have any interest in helping implement the feature?

No.

Code of Conduct

• [X] I agree to follow this project's Code of Conduct
• [X] Have you checked the Contributing document?
• [X] Have you ensured this change was not already requested?

[oruebel]

I think at least moving ExternalResources, ExternalResourceMangager, TermSet etc. codes into a separate module would be useful to do before the release

[mavaylon1]

I'd prefer not. I want to get everything out there now and focus on finalizing tutorials and the talk. @oruebel