[feature/passwords] Move combined hashing methods to manager

This will get rid of the circular dependency between the passwords manager
and the passwords helper. The combined_hash_password() method was also
slightly changed to allow both the definitions of service names or prefixes
for the hash types.

PHPBB3-11610

tests/passwords/manager_test.php

@@ -198,6 +198,10 @@ class phpbb_passwords_manager_test extends PHPUnit_Framework_TestCase
 					array('passwords.driver.salted_md5'),
 					false,
 				),
+				array(
+					'$H$',
+					array('$2a$'),
+				),
 			);
 		}
 		else
@@ -229,6 +233,10 @@ class phpbb_passwords_manager_test extends PHPUnit_Framework_TestCase
 					array('passwords.driver.salted_md4'),
 					false,
 				),
+				array(
+					'$H$',
+					array('$2y$'),
+				),
 			);
 		}
 	}