Stunner - possibility to enlarge a Business Process Canvas

Requirement
For now it is not possible to design complicated large projects in Stunner. Some mechanism to enlarge canvas are needed. For example as it is in current designer: if you move you mouse close to border small yellow arrow will be shown. If you want to enlarge your Process in this way you can click on this arrow and that's it - you process is enlarged.

Solution
After doing some research and talking with others, the conclusion is that reusing the "growable" canvas mechanism, already implemented for GDT, results on the most efficient solution to use in the Stunner based editors, targeting for now only the BPMN process editor, but making it generic for further use as well.

See this solution in action by looking at this example video, posted by manstis@redhat.com, about how the canvas panel size is no longer restricted in GDT.

Technical achievements:

• Identify & understand code behind the classes related to the "growable" canvas/panel in GDT (uberfire-wires)
• Refactor classes as:
  • Decouple from "grid" (GDT) domain
  • Refactor into lienzo modules
• Refactor GDT for using new stuff
• Refactor Stunner base editor/s for using new stuff

Feature achievements:

• Stunner Main Editor
  • Ability to increase/decrease the canvas size on demand
  • Ability to use scrollbars to move around the canvas
  • Performance checks (virtual/real canvas)
• Stunner Preview
  • Ability to scale up/down preview canvas as the main editor grows/shrinks
  • Display the main editor's visible area (rectangle)
  • Update visible area when scrolling happens on the main editor
  • Update visible area when resising happens on the main editor
  • Update main editor's visible position (plus scrollbars) when dragging the visible area (rectangle)
• Canvas Export- Export all virtual canvas (area) and crop the output
• Preferences - Remove use of canvas width and canvas height preferences, those no longer apply.