Add permissions methods to API

This adds /permissions and /permissions/PERMNAME to the API, allowing
retrieval of all permissions and all groups and users that have a given
permission.

This also updates the users and groups API methods to return permissions
with distance/path information. This allows consumers to know more about
the state of permissions.
Add some permissions testing

This adds a tests module for permissions to test their creation,
assignment, and inheritance.
Use fixture for standard graph

Also does some cleanup of imports (don't glob import), cleans up some
dict comprehensions, etc.
Convert to sorted/list compare

This lets us remove some implicit knowledge about the return type being
a set. Now we just return something, sort it, and compare to our sorted
lists. A little saner.
Merge pull request #5 from zorkian/permissions-api

Add permissions methods to API