VMM/account: Integrated class ServiceSet in class Account.
Replaced methods Account.enable() and Account.disable() by
Account.update_serviceset().
VMM/handler: Replaced methods Handler.user_disable() and Handler.user_enable()
by Handler.user_services()
VMM/domain: Integrated class ServiceSet in class Domain.
VMM/handler: Extended Handler.domain_add() and added Handler.domain_services().
Removed unused domain.get_gid import.