Check valid password via service

- Create validation service; fixes same code being duplicated in four places
   - Goal is to remove Utils class, by moving methods to validation service or other services
 - Remove unused properties in legacy settings

src/main/java/fr/xephi/authme/process/Management.java

@@ -41,7 +41,7 @@ public class Management {
     }
 
     public void performRegister(final Player player, final String password, final String email) {
-        runTask(new AsyncRegister(player, password, email, plugin, dataSource, processService));
+        runTask(new AsyncRegister(player, password, email, plugin, dataSource, playerCache, processService));
     }
 
     public void performUnregister(final Player player, final String password, final boolean force) {