#59: add API to check whether a user is invited or not
#59: added the front end to show a status whether or not a user is invited.
- we need to replace this eventually as we are firing a query off per user. The
user object in the API should already return the field so that we only have to make
one trip. The question remains - do we really need a separate collection for
invites? The reason we did it is so we could expire the invite using TTL
in Mongo.
#59: delete existing invitation when deleting a user
#59: add the set password page (WIP)