Allow including and excluding channels

Starting on this now!

As field description for the checkbox please use something like:
"When checked, the given channels will be excluded instead of being included"

Can we have an additional WatchdogMailerMailTest test for the exclude functionality?

Re: #4 the current description is already fine, sorry. I didn't see that.
You may decide to keep it as-is!

Everything's implemented and ready now! (Also implemented the Test, thanks for the reminder!)

Great! :)

Automatically closed - issue fixed for 2 weeks with no activity.