Fixed navigation drawer issues

This should finally fix #11 and #20. This resolves issues with highlighting the current selected item. It also slightly shrunk the height of the large list items; I thought it looked better this way. Screenshot:

![screenshot_2014-05-08-21-57-47 1](https://cloud.githubusercontent.com/assets/1476544/2924008/467b414c-d726-11e3-8f4c-ea5a12ef4cdb.png)