Generalize validation

[CodyCBakerPhD]

fix #1431

Motivation

WIP synchronizing the behavior of the CLI pynwb.validate function with the library-imported one, namely for the purposes of validating against cached namespaces (but also just to have identical behavior between library and CLI use cases).

How to test the behavior?

Need to...

[ ] - Thoroughly test that the CLI usage behaves as it used to
[ ] - The cached namespace feature is indeed available to the new library method as well
[ ] - Ensure there is no break in back-combability when using the previous methods

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change? - a splinter/extension of enh/getcachednamespaces
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[rly]

Related to #1432.

@CodyCBakerPhD can you adjust this PR to branch off of dev? I have some thoughts on the modularize PR #1493. I'd like to get this PR sooner.

[CodyCBakerPhD]

Replaced by #1511