Add a user creation API

Review Request #8185 — Created May 24, 2016 and submitted — Latest diff uploaded

Information

Review Board
release-2.5.x
f90e8bd...

Reviewers

Users can now be created through the /api/users/ endpoint. This is
only available on the global api (i.e, not on any local sites) and to
superusers.

Ran unit tests.