Add lexical validation (spellchecking, punctuation, casing) to OAK

Followed on from #305

- spellchecking (e.g https://github.com/FlyBase/flybase-ontology-scripts/blob/master/misc/obo_spellchecker.py)
- punctuation
- correct casing (e.g. https://github.com/cmungall/capital-offence)

From @gouttegd

> at FlyBase we have a small pronto-based script to do some minimal validation of the text in definitions and comments
> https://github.com/FlyBase/flybase-ontology-scripts/blob/master/misc/obo_spellchecker.py
> It checks spelling and obvious typo mistakes such as missing or duplicated punctuation (it started as a spell-checking script only, hence the name).

Start by reading the follow-up context in issue #305 and the referenced FlyBase spellchecker and capital-offence projects. Define validation coverage for spelling, duplicated or missing punctuation, and casing, then confirm that OAK reports these lexical problems consistently across the relevant text.

Written by the indexing model from the issue text.