Make Render Cache opt-in

There are currently a lot of problems with the render cache. Namely, it doesn't work. While it isn't extremely difficult to fix it, it also isn't trivial. It's also unclear if the benefits are actually still... beneficial.

This PR simply disables the view cache by default. It's been disabled in Shopify for ages anyway, so we know performance is fine. It also makes view caching an option on the config namespace instead of the view prototype, which was weird. You can now use `Batman.config.cacheViews = true` if you want to manually re-enable the view cache.

@kristianpd @pushrax @joshpc