Make dashboard columns configurable (PMT #95949)

This lets the user control how the dashboard is displayed:

![screenshot from 2014-08-07 13 47 33](https://cloud.githubusercontent.com/assets/59292/3846257/2adf3412-1e5b-11e4-90a6-9dc9bfefe13b.png)


Still TODO is figuring out the best way to store this configuration.