Anton/sync groups and verticals

This fixes https://openedx.atlassian.net/browse/BLD-1095

NB: before merge `ENABLE_GROUP_CONFIGURATIONS` should be set to default value.

Please review: @tymofij  @cahrens 

@explorerleslie Sandbox is http://studio.auraz.m.sandbox.edx.org/
Fixed: DEFAULT_GROUP_NAME_PREFIX