canWithdraw() + changes to displayable() (#6902)

* `shouldDiplay()` + `canWithdraw()`

* Better implementation of `displayable()`

core/src/mindustry/ui/Displayable.java

@@ -4,5 +4,9 @@ import arc.scene.ui.layout.*;
 
 /** An interface for things that can be displayed when hovered over. */
 public interface Displayable{
+    default boolean displayable(){
+        return true;
+    }
+
     void display(Table table);
 }