Added string utilities class, fixed some imports

src/main/java/fr/xephi/authme/util/StringUtils.java

@@ -0,0 +1,19 @@
+package fr.xephi.authme.util;
+
+import net.ricecode.similarity.LevenshteinDistanceStrategy;
+import net.ricecode.similarity.StringSimilarityService;
+import net.ricecode.similarity.StringSimilarityServiceImpl;
+
+public class StringUtils {
+
+    public static double getDifference(String first, String second) {
+        if(first == null || second == null)
+            return 1.0;
+
+        StringSimilarityService service = new StringSimilarityServiceImpl(new LevenshteinDistanceStrategy());
+
+        double score = service.score(first, second);
+
+        return Math.abs(score - 1.0);
+    }
+}