Support sorting of rows in the Web API

[llewelld]

User story: "As a user I'd like to be able to sort the rows in the tables shown in the Web interface, so that I can group and order items; this would allow me to better understand the order things happened and also to group together finance codes, tickets, etc."

There are multiple tables shown in the RCTab Web API: Approvals, Allocations, Finance, Cost recovery and Users. It would be useful for many reasons if the rows in the tables could be sorted.

The functionality already exists in the subscription list table (on the main page) and appears to be implemented client-side, so potentially the same approach could be used for the other tables too.