Bug 1106896 - Improve debug and error reporting in mozSettings. r=qdot, a=bajaj

We break down the logging capabilities into two classes: debug and
verbose. Verbose will help to track everything that happens, while debug
should just report error cases. We also augment memory reports with
values to help tracking potential issues like: queue blockage, leaking,
etc.
Bug 1065924 - Make sure we correctly update the variables tracking the number of samples written. r=jesup, a=bajaj