Added support for sorting review requests in the dashboard and various lists (submitters, groups, all). The columns are now clickable and will cause the list to sort.

Up to three columns can be taken into consideration for sorting at any given point. We update the columns when clicked as follows:

* If the column is not in the existing sort list, it becomes the primary sort column and we display a large down arrow.
* If the column is in the existing sort list and is the primary sort column, we reverse the order of the column and display a large up arrow.
* If the column is in the sort list but is not the primary sort column, we make it the primary sort column, and we don't reverse the order.

We save a cookie every time the order changes and use that next time unless a ?sort= parameter is set.

Sorted various columns and messed with each case above. Appears to work correctly.