Basic logging of issues in certificates.

Added reporting some of issues with certificates (around line 451 in monitor.py is readable list of everything I'm looking for). Currently it only prints out list of problems in each certificate and then stats (how many certificates have given error).
I'll add some tests soon, I just want to make sure that code looks reasonable before I write them.
(1) observations should be private.
(2) since it's a map my preference is for the name of the map to include information about the key and the value. I'd suggest observations_by_leaf_index