Memoize the reverseUrl filter using lodash.

The following tests were conducted on a basic page with a few URLs being reversed. This is just from page load. A few minutes interacting with a page, and the filter was being called **tens of thousands** of times. After the optimisations, 20 calls on load and 0 extra after causing a few $digest cycles.

# Before
![](http://i.imgur.com/kE5RfuO.png)

# After
![](http://i.imgur.com/4BwSmZa.png)