Add economic entity interfaces

I decided to add these interfaces, instead of just building upon the User & UserData interface, as support for commerce between clans & users might be something that we want to add in the future in Clans.

Patchwork/src/main/java/me/totalfreedom/economy/EconomicEntity.java

@@ -0,0 +1,8 @@
+package me.totalfreedom.economy;
+
+public interface EconomicEntity
+{
+    EconomicEntityData getEconomicData();
+
+    String getName();
+}

Patchwork/src/main/java/me/totalfreedom/economy/EconomicEntityData.java

@@ -0,0 +1,12 @@
+package me.totalfreedom.economy;
+
+public interface EconomicEntityData
+{
+    long getBalance();
+
+    void addToBalance(final long amount);
+
+    void removeFromBalance(final long amount);
+
+    void setBalance(final long newBalance);
+}

Patchwork/src/main/java/me/totalfreedom/user/User.java

@@ -1,10 +1,25 @@
 package me.totalfreedom.user;
 
+import me.totalfreedom.economy.EconomicEntity;
+import me.totalfreedom.economy.EconomicEntityData;
 import me.totalfreedom.security.PermissionHolder;
 import net.kyori.adventure.text.Component;
 
-public interface User extends PermissionHolder
+public interface User extends PermissionHolder, EconomicEntity
 {
+    // Implement a few EconomicEntity methods in the User interface
+    @Override
+    default String getName()
+    {
+        return getUserData().getUsername();
+    }
+
+    @Override
+    default EconomicEntityData getEconomicData()
+    {
+        return getUserData();
+    }
+
     UserData getUserData();
 
     Component getDisplayName();

Patchwork/src/main/java/me/totalfreedom/user/UserData.java

@@ -1,12 +1,13 @@
 package me.totalfreedom.user;
 
+import me.totalfreedom.economy.EconomicEntityData;
 import me.totalfreedom.security.Group;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import java.util.UUID;
 
-public interface UserData
+public interface UserData extends EconomicEntityData
 {
     @NotNull UUID getUniqueId();