Clean up geometric debugging code for merging.

* Moves more drawing code into draw-protractor.js.
* Adds highlighting of gutter for lines that have geometric
  debugging info.
* Adds line computation for the first 100 events even if they didn't
  cause a visible animation.
* Makes the editor depend on the shared turtlebits.js instead of
  its own jquery.js.  (For future work using the turtle itself for
  geometric debug rendering.)
* Adds a few TODOs for future work to be done.