[UX] Issue #4174 - Add find next / previous buttons for easy navigation


Add next/previous buttons to Find modal bar for easy navigation between matches.

Handles cases
1. Find has matching results
1. Find has no matching results
2. Large documents


![screen shot 2013-06-09 at 7 25 14 pm](https://f.cloud.github.com/assets/1189142/630072/d9e53b42-d18a-11e2-9c35-dc7915ed8a86.jpg)
![screen shot 2013-06-09 at 7 27 06 pm](https://f.cloud.github.com/assets/1189142/630073/d9f980ca-d18a-11e2-80c6-c33c05aed9cc.jpg)
![screen shot 2013-06-09 at 7 27 27 pm](https://f.cloud.github.com/assets/1189142/630074/da0dd516-d18a-11e2-80a5-058c653a1a8f.jpg)
![screen shot 2013-06-09 at 7 30 16 pm](https://f.cloud.github.com/assets/1189142/630075/da13be4a-d18a-11e2-9823-b4a09d70680c.jpg)