Improve alerts (live translation, navigation)

The changes are following:
- Displayed alerts are removed on further navigation
- Alerts are live translated after a language switch

Details:
- It was needed to modify the signature of MessageService.addMessage() method.
- Fix ALV #4249
Merge pull request #10 from alv-ch/#4249-Alerts-werden-nicht-reseted

ref #4249 - Alerts are language changeable, refactored message object, a...