snote when an oper sets/unsets a chm_hidden mode

[jesopo]

trafficstars

setting/unsetting a chm_hidden mode feels like a bit of an event given the only one we've got is chm_operpeace, so I think it makes sense to let everyone know

[jesopo]

this might expose chm_hidden modes to people that have usermode:servnotice but don't have auspex:cmodes

[jesopo]

do we want to do this for chm_staff modes too?

[edk0]

that'd make sense. let's try to send just one notice per /mode though