Additions:
* User command history tracking and querying (`ucHistory`)
* Count total users seen upon connect

Improvements:
* `help` command output, more help for individual commands
* Channel search outputs link to proper Discord channels when available
* Discord bot messaging improvements
* Improve default /whois output
* Start moving command implementations out of userCommands.js
* `mode` command output improved (& fixed), especially for quiet lists

Fixes:
* Channel transform persistence mess has been cleaned up
* Resolve issue #3: PM chan expiry
* Resolve issue #19: Default command character sentinel changed and made configurable (app.allowedSpeakersCommandPrefixCharacter)
* "Is user in channel?" check deferred to allow longer query time
* Simplify live nick tracking and fallback to full query to eliminate false results