A fix to the build and the jump-to-definition feature. Fixes #544, fixes #633

Fixes #544, fixes #633
The normal way of doing something like this, without having to restructure the code and without introducing additional coupling between components, to is to use NetLogo's GUI event system, as documented under “Events” at https://github.com/NetLogo/NetLogo/wiki/Architecture.

I don't see an existing event in https://github.com/NetLogo/NetLogo/blob/5.x/project/autogen/events.txt that you can repurpose for this. So you'd add a new event called something like JumpToDefinitionEvent, raise the event from wherever the UI event is received, and then handle it in `app.Tabs`. For sample code, see how `RuntimeErrorEvent` works; that's an example of an event that automatically brings the Code tab forward.