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.
A comment clarifying why, in this case, a corrupt observation is returned would help understand why in this case the CertificateError exception is handled while not in other cases.