updated styling for marketing side register button to accommodate second line of text - and IE-specific styling

Conflicts:
	lms/envs/dev.py

change over the modulestore configuration to be a dict and use a property accessor. Also update some django-admin configs to use this means to set the runtime configuration

WIP: added a get_modulestore_type. Added some unit tests. changed over the isinstance() with respect to modulestores to use this get_modulestore_type()

add a set_modulestore_configuration to the modulestore interface. This can be used to pass in settings run the Django tier

initial commit for a mixed module store which can interoperate with both XML and Mongo module stores

The django_nose it is very useful, even outside the test
environment. For example, it lets you to easily run test from
manage.py without additional changes to the test packages.

Better wording of commit

Workaround for issue

Better wording of commit

Fixed spacing

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.