fix schema for translated strings

I still need to find a way for generic clients to recognize this in
a sane way!
phpcs fix
add translatable property on schema properties

This is a hack to make it easier for the backend to recognize
i18nized fields that need special handling. I'm extending json
schema like so since i could not find anything resembling a
decent standard that supports this. I'll need to take things like
like this into account when I start validating my schemas against
the yet to be written v5 draft.
change method name
Merge branch 'feature/expose-i18n-in-schema' into develop