Fix various code issues as detected by Sonar

Mostly minor changes:
- Add deprecated javadoc tag on deprecated members
- Reduce duplication (FlatFile, BackupService, ...)
- Make methods static
- Reduce size of anonymous classes
- Replace name with displayName in PermissionsSystemType (avoids confusing with Enum name())
- Tabs to spaces
- Merge if statements

Code from third-party sources (BCryptService, BinTools, PHPBB) not modified.

src/main/java/fr/xephi/authme/security/crypts/PLAINTEXT.java

@@ -1,5 +1,10 @@
 package fr.xephi.authme.security.crypts;
 
+/**
+ * Plaintext password storage.
+ *
+ * @deprecated Using this is no longer supported. AuthMe will migrate to SHA256 on startup.
+ */
 @Deprecated
 public class PLAINTEXT extends UnsaltedMethod {
 

src/main/java/fr/xephi/authme/security/crypts/XAUTH.java

@@ -18,14 +18,14 @@ public class XAUTH extends HexSaltedMethod {
     @Override
     public String computeHash(String password, String salt, String name) {
         String hash = getWhirlpool(salt + password).toLowerCase();
-        int saltPos = (password.length() >= hash.length() ? hash.length() - 1 : password.length());
+        int saltPos = password.length() >= hash.length() ? hash.length() - 1 : password.length();
         return hash.substring(0, saltPos) + salt + hash.substring(saltPos);
     }
 
     @Override
     public boolean comparePassword(String password, HashedPassword hashedPassword, String playerName) {
         String hash = hashedPassword.getHash();
-        int saltPos = (password.length() >= hash.length() ? hash.length() - 1 : password.length());
+        int saltPos = password.length() >= hash.length() ? hash.length() - 1 : password.length();
         if (saltPos + 12 > hash.length()) {
             return false;
         }