Make the weekly digest email configurable as a broadcast message

Particularly while I'm still doing some experimenting and toying with roadmap options, I'd rather that my viewers and reviewers not receive weekly messages about the activity that's gone on with the roadmap.  It may cause them to panic, expecting that there has been lots of change and unilateral decisions when such is not the case.  It feels a bit like you guys are "telling on me" to my audience.  I'd rather have full control of the messaging so that I can manage their expectations better and provide them with updates when it's appropriate.