Additional policies selectable via speed tagging

We allow other policies to be selected at the bottom of the list. The
select box does not contain policies that are shown in the checkbox
list, but only the additional policies that are selected.
Merge pull request #406 from alphagov/all-policies-in-speed-tagging

Additional policies selectable via speed tagging

https://www.pivotaltracker.com/story/show/46254059