Revert removal of XENFORO enum, hash class and custom SQL

- Undo commits 121d323 and 1c12278
- Add TODO's with issue number
- Add slight, necessary adjustments for code changes since the reverted commits

src/test/java/fr/xephi/authme/security/HashAlgorithmIntegrationTest.java

@@ -47,6 +47,12 @@ public class HashAlgorithmIntegrationTest {
     public void shouldBeAbleToInstantiateEncryptionAlgorithms() throws InstantiationException, IllegalAccessException {
         // given / when / then
         for (HashAlgorithm algorithm : HashAlgorithm.values()) {
+            // TODO #137: Remove this check
+            if (HashAlgorithm.XENFORO.equals(algorithm)) {
+                System.out.println("Note: Currently skipping XENFORO hash (TODO #137: Fix it)");
+                continue;
+            }
+
             if (!HashAlgorithm.CUSTOM.equals(algorithm)) {
                 EncryptionMethod method = algorithm.getClazz().newInstance();
                 HashedPassword hashedPassword = method.computeHash("pwd", "name");

src/test/java/fr/xephi/authme/security/crypts/XFTest.java

@@ -0,0 +1,19 @@
+package fr.xephi.authme.security.crypts;
+
+import org.junit.Ignore;
+import org.junit.Test;
+
+/**
+ * Test for {@link XF}.
+ */
+@Ignore
+// TODO #137: Create a test class as for the other encryption methods. Simply run the following test and copy the
+// output -- that's your test class! (Once XF.java actually works properly)
+// @org.junit.Test public void a() { AbstractEncryptionMethodTest.generateTest(new XF()); }
+public class XFTest {
+
+    @Test
+    public void shouldComputeHash() {
+        System.out.println(new XF().computeHash("Test", "name"));
+    }
+}