Add functionality to auto enable new wizard elements

Fixes #1002191
Trigger auto activation of new wizard entries only once
Add constants for Scala file creators to `ScalaPlugin`
Apply reviewer comments

- Move `RichWorkbench` to `EclipseUtils`
- Remove early info logging, because it is not very useful and maybe
  even problematic due to possible deadlocks with stdout redirecting
Merge pull request #755 from sschaef/t1002191-enable-new-wizard-elements

T1002191 enable new wizard elements