[feature/passwords] Use passwords manager service instead of functions

The old functions phpbb_hash() and phpbb_check_hash() have been replaced with
the passwords manager service in all front-end related files. The phpBB2
converter and the release_3_0_5_rc1 migration file have not been changed.
The same applies to the security/hash_test that still tests the function
phpbb_check_hash(). This will however make sure that the old function
still works.

PHPBB3-11610