Refactor world2 to be much more autonomous in generating events, units will usually generate events for things like velocity changes on their own

Additionally, units are refactored to use heading and speed instead of vx and vy
Refactor collision resolution to its own method
Document and further refactor world2
Use the unit's vx and vy properties for stepping them, don't calculate there
Fix a derp, add some nice numerical integration for steps.
Remove explosion on collision test.
Set numerical integration factor to 1, comment exactly what it does
Add blinking to geociites
Remove old world, move world2 -> world
Add stub for map
Merge branch 'develop' into feature-newworld
Fill in Map and Tile classes
Line continuations are important.
Add walls and collisions (mostly) looking natural. Close #29
Allow adding walls to world
Remove map.py
Remove default text in editor
Generate a WallAdded when walls are added to the world
Add a warning to js console on encountering an unknown event
Remove debug print from world