Support for filter event (CollectionViewHelper)

[MichaReiser]

According to the documentation (http://thoraxjs.org/api.html) it should be possible to trigger the filter event on a collection to enforce a refilter of a collection bound to a CollectionViewHelper (with an itemFilter).

Added handling of the filter event of a collection bound to a CollectionViewHelper

[mulderp]

nice one!

[kpdecker]

@eastridge weren't we talking about not supporting this at one time in favor of calls on the collection view itself? My concern with this is you are emitting an event on a potentially shared object that may have only changed for one view.

[MichaReiser]

What about only listening to the event if the collection view has set a filter? For all other instances it's not important anyway. Triggering it on the collection has the benefit, that it's not required to know the CollectionView instance, for example if the collection helper is used...

[kpdecker]

That doesn't really impact the overhead, as applyVisibilityFilter does nothing if there is no itemFilter defined.

At a more conceptual level, this event is saying "hey collection, the view changed, you should tell the view that it changed", which feels wrong to me.

I've run into a number of scenarios where looking up the CollectionView instance was necessary, and somewhat painful to do so I wonder if it would be better to expose an API that makes that easier.

[eastridge]

@kpdecker yes we did talk about that but it was never implemented. This PR makes the code more consistent with the docs but I agree that it's an abuse of what the collection object should be concerned with (using an event on the collection to force something to happen on the view)

[MichaReiser]

I tested 3.x version with getCollectionViews(collection).
This way it's easy to update the view (call updateFilter). Maybe we could add a wrapper to getCollectionViews(collection) to return a composite that offers a updateFilter method with which all views can be updated (_.first(this.getCollectionViews(collection).updateFilter() is somehow complicated...).

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