Class based filtering

[stevin05]

It would be nice to support some form of class-based filtering so that a mail user asking for bracers doesn't trigger a leather bracer alert.

I do pretty regularly get requests from alts asking for their other faction main, so I don't want it to be the default for everything to be class restricted, but maybe add an optional class filter to item keywords? Or might fit better as a filter at the 'category' level so you only have to configure it once to hit all leather/mail gear.