Merge pull request #31 from alphagov/add_url_grouping_drop_down

Add url grouping drop-down to url page
Move placeholder string into options for URL group input

So that we can have different placeholders for different inputs on this page.
Merge branch 'master' of github.com:alphagov/transition into add_user_needs

Conflicts:
	app/views/urls/show.html.erb