Move email verification into PhabricatorUserEditor

Summary: Both email verify and welcome links now verify email, centralize them and record them in the user activity log.

Test Plan:
  - Followed a "verify email" link and got verified.
  - Followed a "welcome" (verifying) link.
  - Followed a "reset" (non-verifying) link.
  - Looked in the activity log for the verifications.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D9284