Adjust to new Breeds architecture, misc updates
- Sprites now can be either data url image or canvas context; shapeToCtx->shapeToImage
- Add once() to model, animator to take a single step/draw pair
- Allow modeler to add/modify layers easily via Model::contextsInit
- Simplified model @contexts handling
- Spotlight simplified; removeSpotlight->setSpotlight(null)
- Fix Model.createBreeds util to manage linkBreeds correctly
- setText/LabelParams: error if agentSetName is not in contexts; adjust for breeds