Allow tables in the UI to be sorted

This should solve #400, allowing tables in Huginn to be sorted by most columns.

Appreciate a code review!

![screen shot 2014-09-10 at 12 10 05 am](https://cloud.githubusercontent.com/assets/83835/4213866/6732bc3e-38bb-11e4-97f6-780d53eda2d7.png)

![screen shot 2014-09-10 at 12 10 17 am](https://cloud.githubusercontent.com/assets/83835/4213867/686a7128-38bb-11e4-86ed-9d6277167816.png)

And you could add `ArgumentError, ` so it is obvious in error traces that it is a programming error.