Modifications to instructor dashboard - enrollment tab:

- Remove single enrollment/unenrollment
- Make unenrollment work with multi-email listbox.
- Provide checkbox for auto-enroll on activate if user not yet signed
up.
- Enroll student when activating if auto-enroll flag set.
Merge branch 'master' of github.com:MITx/mitx into feature-dcadams-usermanagement
Some cleanup.
Merge branch 'master' of github.com:MITx/mitx into feature-dcadams-usermanagement
Merge branch 'master' of github.com:MITx/mitx into feature-dcadams-usermanagement
Fix pep8 violations.
Merge branch 'master' of github.com:edx/mitx into feature-dcadams-usermanagement
Commit just to get Jenkins to rerun.
Merge branch 'master' of github.com:edx/mitx into feature-dcadams-usermanagement
Merge branch 'master' of github.com:edx/mitx into feature-dcadams-usermanagement
Merge branch 'master' of github.com:edx/edx-platform into feature-dcadams-usermanagement
Takes care of Victor's comments on the PR.

Note, the students_lc list is used in _do_enroll_students when overload
= True so it needs to be left in.
Merge branch 'master' of github.com:edx/edx-platform into feature-dcadams-usermanagement
Merge of master to get Jenkins running.
Consolidated coverage report generation into one rake command.
Added diff coverage reports using diff-coverage tool.
Clean the report directories before each test run,
to ensure we don't get coverage results from a
previous test run.
Added diff-cover as a requirement (installed from github)
Merge branch 'master' of github.com:edx/edx-platform into feature-dcadams-usermanagement
Worked on reducing pep8 violations.
Fixed bug in tests.rake in which rm would be called with no args.