Add a fallback route to index.html in development

Ember apps are single-page. Ember appkit requires that you enter the app via index.html or another pre-defined file in public. If you have dynamic URLs, this sucks. You can't just reload a page and be back at the state you were in a moment before.

This adds wildcard middleware to connect. If a file/directory cannot be loaded via the traditional pipeline, then the wildcard picks it up and tries to return index.html or another file configured as the `wildcard` property on the connect options.

So reload that dynamic URL at will, ye masters of Ember.

@stefanpenner, I'm not sure if maybe you had another idea on how to solve this? Or if you solve it elsewhere? IMO this is a good start.