Move locales.js to locale dir

Trying to make it simpler and easier for people to add new translations by
reducing the amount of places where edits need to be made (e.g. no new edits
required in converse.js now).
Add a note to docs about locales.js
Add PO file for Hungarian
Decided to add the JSON files as well

Even though they are actually not used directly and instead a step between the
PO file and generating the .js file
Add hu.js