Add an ACL to User, to allow everyone to execute User.passwordReset().

This is intended to permit users who have forgotten their
password, and are thus unauthenticated, to request a reset.

Credit goes to John Murphy who proposed the ACL in Google Groups here:
https://groups.google.com/forum/#!searchin/loopbackjs/passwordReset$20ACL/loopbackjs/UPyhg7KS-9k/_M_9-YpUKmIJ

Signed-off-by: Carey Richard Murphey <rich@murphey.org>