Testing - initialize data folder in WrapperMock; create ReflectionUtils

- Change AuthMeMockUtils (reflection-based test setup) to ReflectionUtils: service providing reflection functionalities for particular tests where it is appropriate;

- Initialize the data folder (required as soon as the Settings class is loaded) immediately in WrapperMock. Some tests did not set it up that required it and it goes unnoticed if the test is not run individually. This will hopefully fix the tests from failing in the Jenkins build.

src/test/java/fr/xephi/authme/settings/MessagesTest.java

@@ -30,7 +30,7 @@ public class MessagesTest {
      */
     @Before
     public void setUpMessages() {
-        WrapperMock.getInstance();
+        WrapperMock.createInstance();
 
         Settings.messagesLanguage = "en";
         URL url = getClass().getClassLoader().getResource(YML_TEST_FILE);