locking celery version to 3.0.19
Merge pull request #149 from edx/jarv/lock-celery-version

locking celery version to 3.0.19
[sokratik-MVP]

discern working
1. fixtures implemented
2. nginx intergrated
3. email templates fixed
4. flipped to postgres
running discern in new setup

Signed-off-by: himangshu <himangshu@sokratik.com>