Fix indenting on MongoDate change in 2a09f84
Reworking hashing to use PHP built in password_* functions

Uses PHP 5.5 built in password hashing or password_compat implementation
for older PHP versions. Requires PHP 5.3.7, but bcrypt hashing is broken
before then anyway.

RFC for password_* fns: https://wiki.php.net/rfc/password_hash

Also: allow choosing algorithm in config, allow using default cost value
in config