Added search / URL bar

I've added a iOS 7 style dual input field to the navbar. It can be optionally enabled with the ```allowURLEntry``` flag, which defaults to ```NO```;

![ios simulator screen shot 28 nov 2013 17 18 17](https://f.cloud.github.com/assets/5611690/1641322/29838422-5851-11e3-860c-36304f75142a.png)

![ios simulator screen shot 28 nov 2013 17 19 16](https://f.cloud.github.com/assets/5611690/1641326/3aaee8ae-5851-11e3-89be-b99941397e49.png)