Update API description

- Resources are owned by projects, not groups.  (This fixes #157)

- Eventually, we need to add group_add_project and group_remove_project

- It isn't obvious what group-based parameters 'project_create' should take.
  I'm going to leave it taking a single group.  (If it takes no groups, no one
  has the authority to add it to a group, and thus no one can do anything.  It
  may be logical for it to take a list of groups, but that is a larger change,
  so I won't do it now.)
Fix model

The model testsuite passes; the API one fails everywhere.
Fix api.py

All tests now pass, after significant test rewriting.
Fix REST API

The client and server both work now.
Merge pull request #163 from gsilvis/group-fix

Group fix