Refactor: backend translations
Added translations for strings generated/placed in backend (php/twig), this change does not include strings placed directly in js (I have idea for is as well but later on some next refactor).
Includes:
- exceptions,
- table headers (not the one generated automatically, this needs to be reworked),
- forms labels,
- forms placeholders,
- buttons,
- menu elements,
- texts on pages,
- responses,
Additionally:
- changed modules names in menu,