Infection implemented. Still requires testing, and some code clarity work.
Adding tests.
Adds tests for infection initialization, spreading, and clearing in the model.
Image initialization for CellView refactored to take a CellModel.
Merge branch 'feature-visibility' into feature-infection
Small style corrections.
Merge remote-tracking branch 'origin/feature-infection' into feature-infection
Small style nit corrected.
Style nits in testing file.
Merge pull request #31 from zsweedyk/feature-infection

Feature infection