channel bans should store creator and creation time

[slingamn]

stealthgin: hi there, i've setup a fairly default oragono instance and for whatever reason when i set bans on a channel it isn't storing who set the ban or when

[slingamn]

It should be fine to preemptively canonicalize all the masks up front with this before storing them, right?

https://github.com/oragono/oragono/blob/49ba162c7633397cebeab0f436802307cfcaa457/irc/strings.go#L165

[DanielOaks]

@slingamn if we aren't already then yeah definitely