Accumulate churn information into single alert instead of registering multiple

[ChrisSchinnerl]

This is done by introducing an accumulator which is reset every time the alert was dismissed by the user.

Depends on #987

[peterjan]

The churn accumulator is a neat idea, that said I personally still prefer alerts that auto-expire to keep the total number of alerts somewhat in check. By accumulating additions and removals over time you lose some key information like contracts flip-flopping in and out of the set as well as bursts of churn that might coincide with other events. Don't mind though, definitely an improvement 👍