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.

we have data which shows that `get` does not perform well on some browsers. Can we stick to simple method calls.