ziafazal/api-make-org-separate-app: created separate app for organizations

@mattdrayer moved organizations out of api_manager. Created a separated organizations and added a django management command `move_organizations_entries` to move data from existing api_manager_organizations_* table to new tables. organizations app can be enabled via `ORGANIZATIONS_APP` flag. Once data is copied to new tables we can created a migration inside api_manager to remove old tables.