Further abstract Square
Add more specific exceptions to Square
Re-package model tests
Ensure that door was placed on generated grid
Abstract square further
Update TestGridGenerator

The test was written before Pillars and Walls were concrete classes.  It
has been updated to take advantage of this.
Remove unused import
Merge pull request #21 from oharaandrew314/#6-grid-generator

#6 Random Grid Generator
Merge remote-tracking branch 'origin/dev' into #6-grid-loader

Conflicts:
	src/server/controllers/GridGenerator.java