Words conversion extracted to outer 'corrector' gem

== Deletions

* Okei::Word model with a migrations and factory.
* Okei::Words class.
* Okei::Line class.

== Addons

* 'corrector' gem.
* PopulateTranslation AR migration.

== Changes

* the words.json seed divided to words.json, prefixes.json and phrases.json seeds.
Documentation updated