First implementation of search in files

The placeholder text to show when the view is empty still needs to be implemented.

fixed #859

review: @devoncarew

![screen shot 2014-07-19 at 10 43 21 am](https://cloud.githubusercontent.com/assets/332168/3635348/380d40e6-0f6c-11e4-875f-cbbaef91e7cf.png)

`25` is a file result, and `18` is a category (file name)? Can you turn the 25 into a shared constant with the files_controller.dart file? Perhaps in a new dart file in `ui`.