Fix remote config change encapsulation

[jcorbin]

So that each topic funtion does its own noop checking, bounding the complexit of the change dispatcher, and allowing for more nuanced handling of changed keys in a few places.

r @rf @kriskowal

[rf]

:+1:

[kriskowal]

Before and after appear to be consistent. :ok: as long as the reservoir configuration properties are actually independent.