get invite by key
addition of cleanup code

TODO: really need to delete all to start again. If you dismiss and
invite at the mo that means you can’t be sent another. Might need a
policy on that such as old ones are removed once a week
updates to provide err response info

use 404 rather than 204 when item not found for consistency with our
other services
 set a users permissions for given grp

will probably combine with existing method
remove showInvite endpoint as no longer required
remove test now that we no longer have showInvite
Merge pull request #33 from tidepool-org/jhbate/invite

Jhbate/invite