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/main/java/fr/xephi/authme/security/crypts/XF.java

@@ -0,0 +1,74 @@
+package fr.xephi.authme.security.crypts;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class XF implements EncryptionMethod {
+
+    @Override
+    public String computeHash(String password, String salt, String name) {
+        return getSha256(getSha256(password) + regmatch("\"salt\";.:..:\"(.*)\";.:.:\"hashFunc\"", salt));
+    }
+
+    @Override
+    public HashedPassword computeHash(String password, String name) {
+        String salt = generateSalt();
+        return new HashedPassword(computeHash(password, salt, null), salt);
+    }
+
+    @Override
+    public boolean comparePassword(String password, HashedPassword hashedPassword, String name) {
+        // TODO #137: Write the comparePassword method. See commit 121d323 for what was here previously; it was
+        // utter non-sense
+        return false;
+    }
+
+    // TODO #137: If this method corresponds to HashUtils.sha256(), use it instead of this
+    private String getSha256(String password) {
+        MessageDigest md = null;
+        try {
+            md = MessageDigest.getInstance("SHA-256");
+        } catch (NoSuchAlgorithmException e) {
+            throw new RuntimeException(e);
+        }
+        md.update(password.getBytes());
+        byte byteData[] = md.digest();
+        StringBuilder sb = new StringBuilder();
+        for (byte element : byteData) {
+            sb.append(Integer.toString((element & 0xff) + 0x100, 16).substring(1));
+        }
+        StringBuilder hexString = new StringBuilder();
+        for (byte element : byteData) {
+            String hex = Integer.toHexString(0xff & element);
+            if (hex.length() == 1) {
+                hexString.append('0');
+            }
+            hexString.append(hex);
+        }
+        return hexString.toString();
+    }
+
+    @Override
+    public String generateSalt() {
+        // TODO #137: Find out what kind of salt format XF uses to generate new passwords
+        return "";
+    }
+
+    @Override
+    public boolean hasSeparateSalt() {
+        return true;
+    }
+
+    private String regmatch(String pattern, String line) {
+        List<String> allMatches = new ArrayList<>();
+        Matcher m = Pattern.compile(pattern).matcher(line);
+        while (m.find()) {
+            allMatches.add(m.group(1));
+        }
+        return allMatches.get(0);
+    }
+}