USE_CUSTOM_THEME
TODO: make variables ALL-CAPS
Merge pull request #617 from edx/db/add-theme-feature-var

USE_CUSTOM_THEME
Add elasticsearch instances to the cloudformation template.
Update the Elasticsearch subnet CIDR.
Merge pull request #619 from edx/feanil/cloudformation_elastic_search

Feanil/cloudformation elastic search
zipfian specific config
Merge branch 'master' of https://github.com/edx/configuration
added zipfian sass main