Change ModelAttribute's `modelClass` config to `model`, and CollectionAttribute's `collectionClass` config to `collection`. Reorganize some of the code around this, and fix some doc comments as well.
Remove ability for Attribute to take the config 'default' (which is a JS reserved word). Use `defaultValue` instead.
Fix example doc in Model's `get` config.
Fix Collection for possibility that Model dependency is undefined due to circular dependency and load order.
Implement loading pages of data via Collection.loadPage(), and add option to append loaded models (`addModels`) for load() method.