Implement transformation function editor

- text box for manual specification of transformation rules; new task for more sophisticated interaction methods

- premise: working (or passthrough) grammar as base, show warning if error in grammar (transformation function can then still be saved but not live executed)

  • Outputs:
  • parse tree of the function executed against the transformation grammar
  • transformation function also specifies the version of the transformation grammar
  • show transformation end result

(from redmine: issue id 315, created on 2018-01-22tgradl, closed on 2018-01-22)