The files to change were found with:
`ack --literal --type=html --match '${' --files-without-matches cms/templates`

STUD-1312

This commit adds all of cms.

These keys are now objects with a limited interface, and the particular
internal representation is managed by the data storage layer (the
modulestore).

For the LMS, there should be no outward-facing changes to the system.
The keys are, for now, a change to internal representation only. For
Studio, the new serialized form of the keys is used in urls, to allow
for further migration in the future.

Co-Author: Andy Armstrong <andya@edx.org>
Co-Author: Christina Roberts <christina@edx.org>
Co-Author: David Baumgold <db@edx.org>
Co-Author: Diana Huang <dkh@edx.org>
Co-Author: Don Mitchell <dmitchell@edx.org>
Co-Author: Julia Hansbrough <julia@edx.org>
Co-Author: Nimisha Asthagiri <nasthagiri@edx.org>
Co-Author: Sarina Canelake <sarina@edx.org>

[LMS-2370]

* NOTE: the new order is NOT saved to the server!

* update templates and code references
* also a display_name property that defaults to cleaned url_name

Uniquify js fragments pulled from XModules, and load both XModuleDescriptor and XModule js into the cms

Make location into a named tuple, and use it more as a first class entity, rather than URL for identifying content