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.

First phase reviews: @tymofij  @olmar 
This code will be reverted. It is here for now for tests to be run. Most tests for group configuration are decorated with special decorator, which checks for ENABLE_GROUP_CONFIGURATIONS value.