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/util/Utils.java

@@ -54,7 +54,7 @@ public final class Utils {
      *
      * @return the core count
      */
-	public static int getCoreCount() {
-		return Runtime.getRuntime().availableProcessors();
-	}
+    public static int getCoreCount() {
+        return Runtime.getRuntime().availableProcessors();
+    }
 }