LMS-1287

Introduction of the Microsite feature which allows for limited multi-tenant branding on a subdomain basis, e.g. foo.edx.org and bar.edx.org

fix errorenous logic when running a microsite that could reside in a hosting environment with a marketing site in front of it

pep8/pylint fixes

address PR feedback, remove underscore from test hostname

more pep8/pylint cleanup. Skip test_microsites test, it works on localdev, not on Jenkins. Need to talk with QA team

manually add Ned's single-to-double quote fix

change aws.py runtimes so that the microsite_dir that is read from configuration is changed to a python path

Conflicts:
	lms/templates/help_modal.html

into beta dashboard.

Also includes new functionality, in both legacy and beta
dashboard, to include appropriate email text for a
Shibboleth course.

Features coming down the pipe will want to be able to:
* Refer to enrollments before they are actually activated (approval step).
* See what courses a user used to be enrolled in for when they re-enroll in
  the same course, or a different run of that course.
* Have different "modes" of enrolling in a course, representing things like
  honor certificate enrollment, auditing (no certs), etc.

This change adds an is_active flag and mode (with default being "honor").
The commit is only as large as it is because many parts of the codebase were
manipulating enrollments by adding and removing CourseEnrollment objects
directly. It was necessary to create classmethods on CourseEnrollment to
encapsulate this functionality and then port everything over to using them.

The migration to add columns has been tested on a prod replica, and seems to be
fine for running on a live system with single digit millions of rows of
enrollments.