New Browse

First stab at new browse. There are still things to do to make it work correctly but this is a first pass at getting it work. As it doesn't register routes it can't be seen in production but we will be able to manually force preview to show it so we can start testing it.

https://www.pivotaltracker.com/story/show/72442208
Very minor point. Debuggers are still line-oriented, rather than AST-oriented, so I would tend to write this as:

```
if(options.$el.length === 0) {
  return;
}
```

Is that reasoning still valid?