Fix/editor environments
This MR adds some fixes to the Editor in order to handle Environments better.
- An environment's title is not parsed anymore when fetching pages/content, since it is not a straightforward step and it may lead to stripping away important data
- It is now possible to change the type (Definition, Remark, etc.) of an already existing environment on the fly
- Initial support for i18n is added, along with translations of the environment types