Language workbench support

[barnettwilliam]

• [x] #61
• [x] #82
• [ ] Generalise the Xtext editor
• [ ] #84
• [ ] Add features
  • [x] #155
  • [ ] Xtext tool service parallel build
  • [x] #112
  • [ ] UI status feedback (building animations, menu entry hiding on re-build)
  • [ ] Project file copy
  • [ ] Use server sent events to detect editor is ready
  • [ ] Unit tests