Merge pull request #1034 from edx/jarv/clean-ami

Jarv/clean ami
Preview module store.
Adding mapping for preview host.
Removing preview hash gen.
removing preview runtime config.
Deleting legacy templates.
removing unused config.
should be a dict.
Merge pull request #1040 from edx/e0d/preview

E0d/preview
Remove the repo.txt requirements file.
Merge pull request #1125 from edx/feanil/repo_req_release

Feanil/repo req release
Fixing conflict