Add informational requests into json API

[kapsh]

Little fanciness to allow api clients fetch available features.

[supakeen]

Will take a look-see at this one tomorrow as well. For now I notice lexers is plural yet expiry is singular in the routes?

[kapsh]

Agreed, changed this for consistency.

[kapsh]

Sorry, just checked and learned that "expiry" is uncountable word. I will leave it as is, but perhaps you will want to rename related methods later. Every day something new.

Upd disregard that, I don't know English https://www.collinsdictionary.com/dictionary/english/expiry

Word forms: plural exˈpiries
Word forms: plural -ries

[supakeen]

This looks fine, can you please add a testcase for both these routes so I can merge them? A straightforward testcase would be to check if the count of expiries matches what is set in settings. Some examples of how to do testcases are already available in the test/ directory!

[kapsh]

These tests will check that api endpoints return the same data as utilities return.

[supakeen]

Perfect, thank you.