#31 Specify in `PushAnnSpec` whether notes should be announced, i.e. give them an on/off switch

This may be useful because notes form a discussion happening in parallel to IRC, and having it automatically copied into IRC can become annoying spam. There are other ideas, such as reporting notes at most once in X minutes, so that a fast sequence of notes doesn't spam the channel. Either way, I need some feedback from gitlab users to make an good decision.

Closing this for now. I'll wait patiently until someone complains.

Oh, and I did add an on/off switch.