Fixes for Testing as far as Nextcloud 31 installation.

Fixes for Testing as far as Nextcloud 31 installation.

- Ensure ~front~ gets ~front_addr~ by moving it to 192.168.15.3,
  hopefully outside the default DHCP pool.
- Expect ~front~ hostname to be FQDN.
- Don't warn about missing =~/Public/HTML= targets on ~front~.
- Include an alias for ~root~.  This was previously provided by the
  Postfix install.
- Un-truncate the Nextcloud DB password (to match Testing).
- Update Nextcloud installation instructions for version 31, including
  esp. the ~occ maintenance:install~ command and the link to the
  official "Installation from command line" instructions.
- Fix confused syntax in =templates/wild.network=.
- Add forward rules to ~ufw-before-forward~.  ~ufw-user-forward~ is
  reserved for rules generated per user requests.
- Use the Ansible ~ufw~ module to enable the firewall (without
  hanging).
- Fix initialization of ~members~ so that the first member is
  added to an empty hash and not undef.
- Quiet the ~./inst new~ command.
- Removed extra whitespace from many arguments to ~mysystem~ (sorry!).
- Changed name of simulated Internet from ~premises~ (as in the
  introductory diagram) to ~public~ (as in ISP and cloud).
- Statically assign IP addresses to both NICs on ~front~.
- Note need to restart ~gate~ after its first configuration.