Farnsworth format only allows one contact per ID,
so contacts are collapsed by ID and Slot when
generating the JSON. This process is lossy, resulting
in some channels with talkgroups that have names
which don't appear in the final farnsworth output.

To avoid this issue, we pass a mapping of DMR ID
to Talkgroup when generating channels. Instead
of taking the channel's Talkgroup.name as-is,
look up the ID in the set of known contacts and
use the deduplicated name.

Similarly for channels, ensure that GroupList
entries are actually present in the deduped
contact list.

When generating GroupLists, lookup the member
talkgroups by ID to ensure the correct name is
used (after deduping).