Augment needs with as_a, i_want_to, so_that and needotron_id
Create a needotron_id on save
Change needotron_id from integer to string
Enable user needs to added, updated and deleted.
Tidy up following review comments
Put user need form fields on the index page and display 'As a', 'I want to' and 'So that' fields when a user need is selected from the dropdown.
Remove optgroups from user needs dropdown
Don't show content type subtype if it is blank
Add user need id to user needs dropdown
Add Cancel button on user need edit page and display error message if user tries to delete a user need that has associated urls.
Merge pull request #55 from alphagov/everyone_needs_a_thneed

Everyone needs a thneed
Merge commit 'a77e2322e9fd9162681c791f9c575220b251c35b' into HEAD