Move account passwords to shared infrastructure

Summary:
Ref T13043. This moves user account passwords to the new shared infrastructure.

There's a lot of code changes here, but essentially all of it is the same as the VCS password logic in D18898.

Test Plan:

• Ran migration.
• Spot checked table for general sanity.
• Logged in with an existing password.
• Hit all error conditions on "change password", "set password", "register new account" flows.
• Verified that changing password logs out other sessions.
• Verified that revoked passwords of a different type can't be selected.
• Changed passwords a bunch.
• Verified that salt regenerates properly after password change.
• Tried to login with the wrong password, which didn't work.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13043

Differential Revision: https://secure.phabricator.com/D18903