Refactors Score and GameRules class into ScoreKeeper. This will hold all game logic to do with points and scoring. It handles the creation of objects related to points, such as patient severity ratings. It also implements classes for handling game events like delivering a patient, having a patient die while en-route, etc.

This class will be completely decoupled from any other class, so any data that it needs to process scores should be passed into the methods.
Implements basic patient-delivery scoring. OK to merge.
Add dynamic texture loading for patient based on severity level