feat(change_detector): notify directves on property changes

* Changes `WatchGroupDispatcher` to have getMementoGroup function.
* Changes `WatchGroupDispatcher#onChangeRecord` to have signature `onRecordChange(mementoGroup, records:List)`
* Change `ChangeDetector` to group all changes.
* Change `View` to notify directives on changes.

FIELD should not be needed at this point. Can we get rid of it?