Stage.js set up for adaptive creation, but not done yet since Ian wanted to move the forest block sprites around first.
Forest and Castle are now both downloaded by AssetManager and loaded as Stages.
StageTrigger added and put where the old victory screen trigger was. This loads in the next stage.
Some medium-scale refactoring. Got rid of game and ctx fields in entity, as the only time they are used is within draw, during which they can be passed as parameters. Instead, agents now have a game field, in order to get rid of all of the "this.entity.game" nonsense.