Improve the whitelist view

- Add the ability to filter the whitelist table, like the organisations table.
- Add a Cucumber spec to test that only admins can access the whitelist.
- Highlight the row containing the domain just added, so it can be found easily and we can spot typos.
- Add the ability to sort the table by date added, in either ASC or DESC order, using the TableSorter jQuery plugin.

(Rebased today (17th June) against master.)
What does the ID do?