Ex-74 Registration Code redemption

fix the translation issues

added a check if a user is already registered in a course. Changed the messages

added course depth=0 and removed pep8 violations
Fixed bok choy flaky test for studio.
TNL-284
EX-81 / Ex-84 changes
Pyfilesystem fix for AWS
Update translations (autogenerated message)
Merge pull request #5247 from edx/sarina/09162014-translation-update

Update translations (autogenerated message)
Merge pull request #5245 from edx/asadiqbal08/Fix_production_issue

EX-81 / Ex-84 changes
Merge pull request #5207 from edx/waheed/tnl284-fix-flaky-test

Fixed bok choy flaky test for studio.
Merge pull request #5215 from edx/pmitros/pyfilesystem-vpc-fixup

Pyfilesystem fix for AWS. pyfs has broken logic which did not work with AWS roles-based auth. This removes that logic.
Merge pull request #5050 from edx/muhhshoaib/Ex-74-registration-code-redemption

Ex-74 Registration Code redemption
Video link obfuscation. [BLD-1230]
allow TAs to select the cohort of new posts.

TNL-153
Merge pull request #5227 from edx/jsa/tnl153

allow TAs to select the cohort of new posts.
Merge pull request #5059 from edx/anton/add-video-context-menu

BLD-1230: Video Link Obfuscation
Clean up translated strings in registration page, dashboard, and track selection flow