Tested-by / Reported-by credits and more

Tested-by / Reported-by credits and more

Add tracking of tested-by, reported-by, and reviewed-by.  For the first
two, we also track who is *giving* those credits.

While I was in the neighborhood I also:

 - Started turning the "patch" class into something more than a bare
   container; this work has just begin.

 - Moved the report-writing code into its own file (reports.py)