Added getter and setter for maxWidth and maxHeight for button groups.

lib/pixi/buttongroup.js

@@ -371,6 +371,34 @@ export default class ButtonGroup extends PIXI.Container {
         this.buttons.forEach(it => (it.disabled = value))
     }
 
+    /**
+     * Gets or sets the maximum width of the button group for stacking. Usefull when you want to resize the available space.
+     *
+     * @member {number}
+     */
+    get maxWidth() {
+        return this.opts.maxWidth
+    }
+
+    set maxWidth(value) {
+        this.opts.maxWidth = value
+        this.layout()
+    }
+
+    /**
+     * Gets or sets the maximum height of the button group for stacking. Usefull when you want to resize the available space.
+     *
+     * @member {number}
+     */
+    get maxHeight() {
+        return this.opts.maxHeight
+    }
+
+    set maxHeight(value) {
+        this.opts.maxHeight = value
+        this.layout()
+    }
+
     /**
      * Searches all buttons of the button group and returns the maximum width of one button.
      *