---
- group_variables: variables = GET groups/:group_id/variables?
- group_variable: variable = GET groups/:group_id/variables/:variable_key
- create_group_variable: variable = POST groups/:group_id/variables?
- edit_group_variable: variable = PUT groups/:group_id/variables/:variable_key?
- delete_group_variable: DELETE groups/:group_id/variables/:variable_key