[sir-complainsalot] Add grace period and dry run

[krivard]

• A method for sir-CAL to complain that's not blasting Slack, for testing purposes
• The ability to tell sir-CAL not to bug anybody until results are N days late, for configurable N (currently global, might consider per-source or per-signal versions if we need them)

[capnrefsmmat]

Looks good. Not sure why you have grace instead of adding to the lag allowed for the sources in the params; just an easy way to change all of them at once?

[krivard]

That, but also to distinguish between when we usually expect a signal to become available, when it's nominally late but not worrisome, and when somebody should really take a look.