Translation & secure-aware changes to studio's settings page

1. Change the link of course's about page secure aware, which displays 'https' or 'http' prefix according to the current protocol.
2. Make the email in this page translatable.
Merge pull request #4867 from louyihua/localization-cms

Translation & secure-aware changes to studio's settings page
Added a relaunch invitation template email
Merge pull request #4865 from edx/ahodges/doc/DOC815

Added a relaunch invitation template email
Rewrite course url matcher to not be greedy
LMS-11181
Make it branch agnostic
LMS-11210

Conflicts:
	common/lib/xmodule/xmodule/modulestore/split_mongo/split_draft.py
Merge pull request #4878 from edx/dhm/split_branch_agnostic

Make it branch agnostic
Merge pull request #4877 from edx/dhm/course_id_pattern

Rewrite course url matcher to not be greedy
AUTHORS update
Add HTTP_RANGE compatibility for ContentStore file streaming

Currently, users can only download ContentStore files from first byte to
last byte.

With this change, when a request to the ContentStore includes the HTTP
"Range" parameter, it is parsed and StaticContentStream will stream the
requested bytes.

This change makes possible to stream video files (.mp4 especially) from
the ContentStore. Users can now seek a specific time in the video
without loading all the file.

This is useful for courses with a limited number of students that
doesn't require a dedicated video server.