support placeholder api in messages and requirement placeholders in the title

src/main/java/sh/okx/rankup/Rankup.java

@@ -127,6 +127,8 @@ public class Rankup extends JavaPlugin {
       autoRankup.runTaskTimer(this, time, time);
     }
 
+
+
     if (config.getInt("version") < 3) {
       getLogger().severe("You are using an outdated config!");
       getLogger().severe("This means that some things might not work!");

src/main/java/sh/okx/rankup/gui/Gui.java

@@ -50,10 +50,10 @@ public class Gui implements InventoryHolder {
     gui.cancel = cancel;
 
     Inventory inventory = Bukkit.createInventory(gui, items.length,
-        plugin.getMessage(oldRank, gui.prestige ? Message.PRESTIGE_TITLE : Message.TITLE)
-            .replaceRanks(player, oldRank, rank)
-            .replaceFromTo(oldRank)
-            .toString());
+        plugin.replaceMoneyRequirements(
+            plugin.getMessage(oldRank, gui.prestige ? Message.PRESTIGE_TITLE : Message.TITLE)
+                .replaceRanks(player, oldRank, rank)
+                .replaceFromTo(oldRank), player, rank).toString());
     inventory.setContents(items);
     gui.inventory = inventory;
     return gui;

src/main/java/sh/okx/rankup/messages/MessageBuilder.java

@@ -1,5 +1,7 @@
 package sh.okx.rankup.messages;
 
+import me.clip.placeholderapi.PlaceholderAPI;
+import org.apache.commons.lang3.Validate;
 import org.bukkit.Bukkit;
 import org.bukkit.ChatColor;
 import org.bukkit.command.CommandSender;
@@ -24,7 +26,9 @@ public class MessageBuilder {
   }
 
   private static MessageBuilder of(ConfigurationSection config, String message) {
-    return new MessageBuilder(ChatColor.translateAlternateColorCodes('&', config.getString(message)));
+    String string = config.getString(message);
+    Validate.notNull(string, "Configuration message '" + message + "' not found!");
+    return new MessageBuilder(ChatColor.translateAlternateColorCodes('&', string));
   }
 
   public MessageBuilder replace(Variable variable, Object value) {
@@ -99,7 +103,11 @@ public class MessageBuilder {
   }
 
   public void send(CommandSender sender) {
-    sender.sendMessage(message);
+    String msg = message;
+    if (sender instanceof Player) {
+      msg = PlaceholderAPI.setPlaceholders((Player) sender, msg);
+    }
+    sender.sendMessage(msg);
   }
 
   /**