Refactor errorhandler

- [x] Moved all ErrorHandling methods from Application to ErrorHandler
- [x] split errorhandler into two components, base and web.
- [x] fixed some minor issues in web display
- [x] improved error output on console
- [x] fix setup of errorhandler in app init()
- [ ] ~~check how ErrorHandler reacts to error_reporting setting~~

fixes #1946, fixes #2516 

looks like tests are failing because it was February last month :-)