Extract certificates to their own database table

[daveschaefer]

We currently duplicate a lot of information storing the certificate fingerprint inside the observations table. We should move our data back to Third Normal Form and move cert info into it's own table.

[daveschaefer]

In my test with a copy of notary1's data this shrunk the database size by 66%. This would also allow us to properly store other information about certificates, as mentioned in #9 .

[daveschaefer]

Leaving this until we have implemented TLS functionality may be nice, as then the existing v2 notaries could be upgraded with only one set of table changes. They could then be upgraded again with another schema change later.

[daveschaefer]

As per #19, if we plan to implement https mostly by using another server in front of cherrypy, then waiting for HTTPS functionality before we change the database structure isn't the best order of priorities. We should fix the database structure sooner so that we can begin using new hashes ( #22 ).