R1:dd70c5946505

Use OpaqueEnvelopes for all passwords in Phabricator

Summary:
See D2991 / T1526. Two major changes here:

- PHP just straight-up logs passwords on ldap_bind() failures. Suppress that with "@" and keep them out of DarkConsole by enabling discard mode.
- Use PhutilOpaqueEnvelope whenever we send a password into a call stack.

Test Plan:
- Created a new account.
- Reset password.
- Changed password.
- Logged in with valid password.
- Tried to login with bad password.
- Changed password via…