Update Lo-Dash to 2.4.0
Add `isLoading()` as an abstract method on DataComponent.
Clean up Collection.isModified() tests a bit, and tweak Collection class doc.
Re-add data.persistence.request.Batch class. This may be used after all to batch Collection.sync() requests.

This reverts commit 3a12031c689987b4db526cca964ce339f40c3188.
Add getCreateRequests(), getUpdateRequests(), and getDestroyRequests() to data.persistence.request.Batch class.
Add getNewModels(), getUpdatedModels(), and getRemovedModels() methods to Collection. Also clean up some tests.
Change docs in Model/Collection classes to use the term "map" instead of "hash".
Change how Proxies interact with their given Request object. Instead of returning a new Deferred object from each of the CRUD methods of the Proxy, the Proxy now resolves or rejects the Request itself.

Also add `batch()` method to Proxy, which handles multiple create/update/destroy requests at once.