VMM/Transport: reworked Transport class.
Use assertions for argument checks. Removed methods getID() and
getTransport(). This values are now accessible through the read-only
attributes id and transport.
VMM/{Account,Domain}: adjusted to modifications in Transport class.
A few code cleanups.
Config
   cfs - configset sect.opt val
   cfg - configget sect.opt
   ds - domainservices: smtp pop imap sieve???
- Aliases
    - avoid looping aliases
- Domain
    - optional limits for number of:
        + accounts
        + aliases
        + destinations/alias
        + alias domains