i18n support: add multi language support for element label, definitions and usage notes
## Abstract
This issue requests to add multi language support for the content in STH.
This issue is **not** about Semenatic Treehouse UI itself. Maybe that should be a separate issue, but I think English is fine so far.
## Context
Customers, e.g. Ketenstandaard, have to deal with user community that prefers terminology of the standards in their own language (e.g. Dutch), while at the same time international software developers need to interpreted the standards as well.
## What to do:
- [ ] Adapt STH model and database fields to support multilanguage support (element label, definition and usage notes)
- [ ] Add functionality in UI to select preferred language
- [ ] Show other languages in STH UI as well (e.g. in details view of Element)
- [ ] Adapt FIT wizard to copy multi language from ontology
- [ ] ..
issue