Check project against valid and deprecated trove classifiers. (#2881)

Inspects trove classifiers on `check` CLI command calls, and look for
unrecognized and deprecated categories.

Adds dependency https://github.com/pypa/trove-classifiers, a package
published and maintained by the PyPA that is cataloguing all classifiers.
This is the canonical source of all trove definitions.

Resolves: #2579