Add support for /WHOIS, /SWHOIS, and /WHOWAS commands.

These will print output to the target user's message window,
rather than the server messages window, using NOTICE styling.
Tests are included to make sure all the 3xx and 671 messages
are parsed and formatted properly.

Also change 301 (AWAY reply) to go to that window in the same
style, since it often comes through in WHOIS (or SWHOIS)
results. This helps it stand out as a notice from the account,
rather than formatting like a PRIVMSG.

These new messages are created by custom message events in a
new ServerResponseHandler._emitUserNotice() helper function.

While here, reformat server_message_handler.js to have more
readable comments, and collapse some old CoffeeScript leftovers
into more idiomatic JS code.

Resolves issue #171.