WIP: Add failing IT for sending invite
WIP: Added a service for dealing with ExpiringCode. Creating user up
front without a password when an invitaiotn is made. When completing the
invitaiton, we still need to update the user's password and set
verified=true

Signed-off-by: Madhura Bhave <mbhave@gopivotal.com>
[#77649296] Add ability to send and accept invitations in the login server.

https://www.pivotaltracker.com/story/show/77649296
Signed-off-by: Rob Szumlakowski <rszumlakowski@pivotal.io>
Reinviting an existing unverified user sends another invitation email
 - Inviting an existing verified user will display a error message
 
 [#81207058 finished] https://www.pivotaltracker.com/story/show/81207058
Merge branch 'feature/invitations' into develop