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.
I suggest getting rid of severity entirely:
(1) It's a subjective measure (not everyone who looks at certificates will consider violation X to be more severe than violation Y).
(2) It makes the code messy (have to implement your own comparison and hash operators).