Add fuzzy search field

This adds a simple text field to the page that filters through tweets to show those that match that particular text in content or user.

![screenshot 2014-12-11 16 04 51](https://cloud.githubusercontent.com/assets/2766324/5402147/8a6c3cd4-814f-11e4-8405-e76ca090daf2.png)

@ndelage - any thoughts on this code?
While searching on `keyup` without any hesitation is totally appropriate here, this is a great time to introduce underscore's `_throttle` & `_debounce` helper methods: http://underscorejs.org/#throttle