Implement the election admin groups

This allow the election admin creating the election to specify multiple
FAS groups which will be able to view the results before they are made
public without having to add them to the election admin group itself
Make the tests pass offline
Elections admins are now admins of every elections
Enhance coverage of the is_admin function
Specify an admin group for the election #2
Test the is_election_admin when the user is and is not in an AdminGroup of that election
Sort the election's admin groups
Add unit-test testing the addition and removal of admin groups when editing an election
Add unit-tests for the is_safe_url method
pep8 fixes
Explain a little what the admin groups are
Merge pull request #23 from fedora-infra/election_admins

Election admins