Display only the current route

This is helpful when you have enough routes that you can't even see the
current one.

The current view looks like this:

![ember-inspector-all-routes](https://cloud.githubusercontent.com/assets/743977/3682666/2cde551a-12d3-11e4-95e7-48e2e8e54b59.png)

And when using the option

![ember-inspector-current-route](https://cloud.githubusercontent.com/assets/743977/3682668/3695f644-12d3-11e4-908b-d966afa35591.png)