Move VerifySyncInfo from TimeoutRuler to cert.Authority

[meling]

Fixes #262

This moves the VerifySyncInfo logic from the simple and aggregate timeout rules into a common logic on the cert.Authority struct, along with many other crypto verification methods (also used by the VerifySyncInfo method). This also removes the method from the TimeoutRuler interface, reducing the interface to only two methods.

Since the Simple and Aggregate timeout rules now share a common VerifySyncInfo method, the tests no longer matched the previous expectation. However, I believe these changes match the expectations for advancing the view when we have only one of AC or QC.