Fixed #106. POSTing to scans requires user.

We want to display the user started the scan in the frontend, and we
have to add user (oriignally called owner) in the POST and have
summary_scan(..) to return 'meta' as part of the summary.
Fixes #112 The plans API should not return plugin descriptors
Merge pull request #108 from yeukhon/issue106

Issue106
Removed test_api.py. I think it got accidentally added back after splitting up the tests.
Fixed #109. Users collection has a status field.

We now have an option to either mark a user active via direct signup, or
mark a user as invited via invitation. Bad users can be marked as
'banned'. When a user is marked as invited, the user is given a url
(front-end) to login. Upon the first login, the status will change to
'active'. Ticket #111 will check user's status and prevent banned users
(and non-active) users from accessing Minion.
Added SMTP call so POSTing to /users can send invitation. See #110.
Update README.md to include postfix as dependency.
Update setup.py to include minion-db-init.
Added POST /invites. See #114.
Added GET /invites with basic filters. See #114.
Merge branch 'issue109110' of https://github.com/yeukhon/minion-backend into issue109110

Conflicts:
	minion/backend/api.py