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

Feanil/repo req release
Make devpi optional for edxapp

To enable, set the `edxapp_devpi_enabled` variable to `true` and set
edxapp_pypi_local_mirror to point to wherever devpi is installed.
Add devpi_host setting to devpi role

Allow specifying a different host than localhost.
Add flag to disable/enable New Relic

Set to 'false' to disable.
Add npm mirror URL

Allow to set a custom npm local mirror (e.g sinopia).