Fix oauth client redirect_uri handling #211

- Make the redirect_uri comparison slightly loosing (case insensitive)
- For clients that have a redirect_uri without a http and domain, add the
current api domain.
- Update the migration script which creates our default client - always set 
redirect uri to "/". The actual base url will get appended later. This ensure
the ushahidiui client can only ever be used to authorize the ui not some other
server.