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.
There is already default description in InvalidCharacter, if I set reason to '' then it will be printed as:
"dNSNames: Invalid character : () [asdf*, asdf*, 4]" or something like that, while if reason is None then () will be skipped. So I think it's better this way.
tl;dr reason = None instead of something else is intended.