Add Url group using jquery dialog on url page
Merge
Clear dialog form when Cancel is clicked
Merge branch 'master' of github.com:alphagov/transition into add_url_group

Conflicts:
	app/views/urls/show.html.erb
Don't pre-select added url group if dropdown is readonly.
Display a message indicating that no urls have been loaded instead of 500 page
Address review comments
Merge pull request #58 from alphagov/add_url_group

Add url group using a jquery dialog