Event name filtering for sources

[sethetter]

For some sources, we may want to be able to filter the events we promote to channels based on their name or some other data.

[sethetter]

Maybe it would be better to implement this at the rule level? Events could be filtered on a per-event and per-channel basis, giving much more granular control.

[sethetter]

If we do it at the rules level, perhaps we return an extra boolean param from the MsgFunc which acts as a signal to not send a message under certain circumstances?