Use UAA's transaction endpoints for create/update/delete of clients

Includes some refactoring of:
- ServiceBrokerRemoval => ServiceBrokerRemover
- uaa command interface changed from apply! to db_command and
  uaa_command
Add ssl support when modifying dashboard clients with UAA.
Handle 404 when requesting token from UAA
Return meaningful errors when the UAA returns an error during
create/update/delete service-broker