Save and re-use views from memory store

[eleventigers]

When view are created via Handlebars view helper, they are added to a memory store like models and collections. Later when BaseView tries to re-attach views to DOM it looks up memory store for the same name view.
I am not sure if using fetcher to hold viewStore is a good idea as fetcher mainly deals with serializeable data. Any ideas where we could store views?

[spikebrehm]

We wouldn't need preventPostInitialize anymore, right?

[spikebrehm]

I like the approach, however I don't think it's appropriate to use MemoryStore for this; there's no point in holding on to instances of the view after we're done rendering & attaching. If we keep an instance in the store for every view, pretty soon we'll run out of memory after using the app for awhile. It could be a bit simpler to have a ViewStore that purges the cached value after it's been grabbed from the cache.