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/util/ValidationService.java

@@ -0,0 +1,42 @@
+package fr.xephi.authme.util;
+
+import fr.xephi.authme.output.MessageKey;
+import fr.xephi.authme.settings.NewSetting;
+import fr.xephi.authme.settings.properties.RestrictionSettings;
+import fr.xephi.authme.settings.properties.SecuritySettings;
+
+/**
+ * Validation service.
+ */
+public class ValidationService {
+
+    private final NewSetting settings;
+
+    public ValidationService(NewSetting settings) {
+        this.settings = settings;
+    }
+
+    /**
+     * Verifies whether a password is valid according to the plugin settings.
+     *
+     * @param password the password to verify
+     * @param username the username the password is associated with
+     * @return message key with the password error, or {@code null} if password is valid
+     */
+    public MessageKey validatePassword(String password, String username) {
+        String passLow = password.toLowerCase();
+        if (!passLow.matches(settings.getProperty(RestrictionSettings.ALLOWED_PASSWORD_REGEX))) {
+            return MessageKey.PASSWORD_MATCH_ERROR;
+        } else if (passLow.equalsIgnoreCase(username)) {
+            return MessageKey.PASSWORD_IS_USERNAME_ERROR;
+        } else if (password.length() < settings.getProperty(SecuritySettings.MIN_PASSWORD_LENGTH)
+            || password.length() > settings.getProperty(SecuritySettings.MAX_PASSWORD_LENGTH)) {
+            return MessageKey.INVALID_PASSWORD_LENGTH;
+        } else if (settings.getProperty(SecuritySettings.UNSAFE_PASSWORDS).contains(passLow)) {
+            // TODO #602 20160312: The UNSAFE_PASSWORDS should be all lowercase
+            // -> introduce a lowercase String list property type
+            return MessageKey.PASSWORD_UNSAFE_ERROR;
+        }
+        return null;
+    }
+}