Finalized some fields, removed redundant code, various other fixes

src/main/java/fr/xephi/authme/cache/auth/PlayerAuth.java

@@ -16,7 +16,7 @@ public class PlayerAuth {
     private double z;
     private String world;
     private String salt;
-    private int groupId;
+    private final int groupId;
     private String email;
     private String realName;
 

src/main/java/fr/xephi/authme/cache/auth/PlayerCache.java

@@ -7,7 +7,7 @@ import java.util.concurrent.ConcurrentHashMap;
 public class PlayerCache {
 
     private volatile static PlayerCache singleton;
-    private ConcurrentHashMap<String, PlayerAuth> cache;
+    private final ConcurrentHashMap<String, PlayerAuth> cache;
 
     private PlayerCache() {
         cache = new ConcurrentHashMap<>();

src/main/java/fr/xephi/authme/cache/backup/DataFileCache.java

@@ -4,9 +4,9 @@ package fr.xephi.authme.cache.backup;
  */
 public class DataFileCache {
 
-    private String group;
-    private boolean operator;
-    private boolean flying;
+    private final String group;
+    private final boolean operator;
+    private final boolean flying;
 
     /**
      * Constructor for DataFileCache.

src/main/java/fr/xephi/authme/cache/limbo/LimboCache.java

@@ -19,9 +19,9 @@ import java.util.concurrent.ConcurrentHashMap;
 public class LimboCache {
 
     private volatile static LimboCache singleton;
-    public ConcurrentHashMap<String, LimboPlayer> cache;
-    public AuthMe plugin;
-    private JsonCache playerData;
+    public final ConcurrentHashMap<String, LimboPlayer> cache;
+    public final AuthMe plugin;
+    private final JsonCache playerData;
 
     /**
      * Constructor for LimboCache.

src/main/java/fr/xephi/authme/cache/limbo/LimboPlayer.java

@@ -8,7 +8,7 @@ import org.bukkit.scheduler.BukkitTask;
  */
 public class LimboPlayer {
 
-    private String name;
+    private final String name;
     private Location loc = null;
     private BukkitTask timeoutTaskId = null;
     private BukkitTask messageTaskId = null;