nixos: resolve uid/gid conflicts

This patch resolves all uid/gid conflicts except for nobody/nogroup (seems
to make sense that these are the same).
All conflicts where determined mechanically, but resolutions were manual.
This patch also marks uids/gids with no corresponding group/user as "unused"
(aka. reserved).

Briefly,

- tss group conflicts with dhcpcd
  The tss group id conflicts with dhcpcd: assign
  a new number and add a corresponding tss user.
- elasticsearch uid conflicts with haproxy gid
- resolve firebird/munin conflict
- fix fourstorehttp{,d} typo
- fix ghostOne typo: the service module refers to gids.ghostone, so use that
  in ids
- memcached uid conflicts with users gid
- nagios uid conflicts with disks gid
- nscd uid conflicts with wheel gid
- ntp uid conflicts with tty gid
- resolve postfix/postdrop id uid
- redis uid conflicts with keys gid
- sshd uid conflicts with kmem gid
- tcryptd uid conflicts with openldap gid
- unifi uid conflicts with docker gid
- uptimed uid conflicts with utmp gid
- zope2 uid conflicts with connman gid
- tomcat uid/gid mismatch