Additional Work 8/27/2017

A lot of work on the internal code, cutting up the model into smaller bits, moving some of it into other classes where possible, moving others into Game class methods.

Put all creeps into a creep library so that they're no longer generated on the fly in the model.  Evolution has been moved into the creep objects and currently depends on the wave number; when the board expands more slowly later on (based on base size), I'll base the hits on the wave number and the speed on the board size.

Moved a lot of the site and source generation code into 

Added cursor controls with the arrow keys.  Need to add more keyboard shortcuts for buying and selling towers.