[SCHEMA] Store raw remote contact data.

Summary:
Right now we're just keeping a few fields in the contacts schema. By keeping
the entirety of the data we get from the remote provider, we can revise the
schema without resyncing.

Test Plan: Behavior manually verified for Google contact sync.

Reviewers: mg

Reviewed By: mg

Differential Revision: https://review.inboxapp.com/D93