Test more tagging functionality

Summary:
Charles,

I've added two test cases for tagging, one about archiving and the other about marking as spam and trashing.
The latter crashes the syncback service with a NotImplementedException. I'll look into fixing this.

Could you tell me what you think of the code? Do you have other ideas for tagging test cases?

Test Plan: Ran the tests. Checked that they (mostly) passed.

Reviewers: charles

Reviewed By: charles

Differential Revision: https://review.inboxapp.com/D441