IRCConnection: sort users by their mode and their nickname

Currently, users are only naturally sorted which leaves their prefixes
in the mix. While this gets the ordering of users correct, it also
neglects the priority of their prefixes. For a cleaner looking sort,
users should first be sorted by their prefix, and then by their
nicknames.

Signed-off-by: jgeboski <jgeboski@gmail.com>
Merge pull request #11 from jgeboski/improve-user-sort

IRCConnection: sort users by their mode and their nickname

-> Add an option for how things should be sorted and such.