This change adds support for adding reviewers by email in PostReviewer
and ChangeInfo. It also adds support for deleting reviewers using the
ReviewerResource by adding Address to it.
It further adds support for sending emails to reviewers that were
added by email. This support includes emails for adding and removing a
reviewer as well as for general change notifications.
This change also adds tests and updates the documentation.
Bug: Issue 4134
Change-Id: I901d711956ee69c25a05b455e068ec109821d79d
11873ef74e