plugins/irc: minor refactor of channel status checking
add support for server commands via IRC.

if a user on IRC has the required channel status, they can use the
syntax "!command" from IRC to enter a command in the server's console
(by default there is no status so nobody can execute commands). can be
configured to allow a certain list of commands. if enabled, !~command
from IRC will run a mark2 command.
update mark2.default.properties for 265f422
update documentation for plugins/push