Implement !battlepass command

Examples:
`!battlepass premium` = Activates elite grant
`!battlepass lv40` = Unlocks the rewards up to level 40

src/main/java/emu/nebula/command/commands/BattlePassCommand.java

@@ -0,0 +1,61 @@
+package emu.nebula.command.commands;
+
+import emu.nebula.command.Command;
+import emu.nebula.command.CommandArgs;
+import emu.nebula.command.CommandHandler;
+import emu.nebula.net.NetMsgId;
+
+@Command(label = "battlepass", aliases = {"bp"}, permission = "player.battlepass", desc = "/battlepass [free | premium] lv(level). mMdifies your battle pass")
+public class BattlePassCommand implements CommandHandler {
+
+    @Override
+    public String execute(CommandArgs args) {
+        // Get target
+        var target = args.getTarget();
+        var battlepass = target.getBattlePassManager().getBattlePass();
+        boolean changed = false;
+        
+        // Check if we are changing premium status
+        int mode = -1;
+        
+        for (var arg : args.getList()) {
+            if (arg.equalsIgnoreCase("free")) {
+                mode = 0;
+            } else if (arg.equalsIgnoreCase("premium")) {
+                mode = 2;
+            }
+        }
+        
+        if (mode >= 0 && battlepass.getMode() != mode) {
+            battlepass.setMode(mode);
+            changed = true;
+        }
+        
+        // Set level
+        int level = Math.min(args.getLevel(), 50);
+        
+        if (level >= 0 && battlepass.getLevel() != level) {
+            battlepass.setLevel(level);
+            changed = true;
+        }
+        
+        // Check if we have made any changes
+        if (changed) {
+            // Save battle pass to the database
+            battlepass.save();
+            
+            // Send package to notify the client that the battle pass needs updating
+            target.addNextPackage(
+                NetMsgId.battle_pass_info_succeed_ack, 
+                battlepass.toProto()
+            );
+            
+            // Success message
+            return "Changed the battle pass successfully.";
+        }
+        
+        // Result message
+        return "No changes were made to the battle pass.";
+    }
+
+}

src/main/java/emu/nebula/game/battlepass/BattlePass.java

@@ -30,7 +30,7 @@ public class BattlePass implements GameDatabaseObject {
     private int uid;
     private transient BattlePassManager manager;
     
-    private int battlePassId;
+    private int battlePassId; // Season id
     private int mode;
     private int level;
     private int exp;
@@ -71,6 +71,13 @@ public class BattlePass implements GameDatabaseObject {
         return manager.getPlayer();
     }
     
+    /**
+     * Sets the mode directly
+     */
+    public synchronized void setMode(int mode) {
+        this.mode = mode;
+    }
+    
     public boolean isPremium() {
         return this.mode > 0;
     }
@@ -79,6 +86,14 @@ public class BattlePass implements GameDatabaseObject {
         return GameData.getBattlePassRewardDataTable().get((this.getBattlePassId() << 16) + level);
     }
     
+    /**
+     * Sets the level directly, use getMaxExp() instead if adding exp.
+     */
+    public synchronized void setLevel(int level) {
+        this.level = level;
+        this.exp = 0;
+    }
+    
     public int getMaxExp() {
         var data = GameData.getBattlePassLevelDataTable().get(this.getLevel() + 1);
         return data != null ? data.getExp() : 0;