希望脑图编辑组件呈现横纵滚动条

虽然现在鼠标滚动以及右键拖动能实现上下左右滚动，但是在实际操作中还是有些不方便，Xmind是直接实现横纵滚动轴的，如果能保持与Xmind一致，对Xmind使用者也有良好的体验，希望能考虑一下这个需求

Locate the mind-map editor entry point and inspect how mouse-wheel and right-button dragging currently provide horizontal and vertical scrolling. Add visible horizontal and vertical scrollbars with behavior consistent with XMind. Done means users can scroll the editor in both directions directly with the scrollbars.

Written by the indexing model from the issue text.