Validate Certification of Update Calls

[hansl]

Currently blocked by https://github.com/dfinity-lab/ic-ref/pull/90

[nomeata]

Also see https://docs.google.com/document/d/1MJ4LUDJt_29xws36af78RKSfzui9PYKsT20nWVUhqig/edit#

[nomeata]

JFTR: Seems to be worked on in #70 and #68

[nomeata]

This is done, right?