mpl widgets: LassoSelector/RectangleSelector

Hi,

I build a backend for this package in vaex, so vaex is showing many rows/particles in this matplotlib backend. However, I'd like to select things using the lasso or rectangular selector, the rectangular works ok, it draws sth on the screen (see also screenshot). To enabled it I used a ipywidget togglebuttons, but it doesn't play nice with the other buttons (for instance, how would I switch between zoom rectangle and the rectangleselector?). And the lasso selector doesn't draw anything on the screen. Would be really nice to have this, it would be the first time you could do a lasso selection in the notebook to do a freehand selection for ~1 billion rows.

检查 vaex/notebook/ipympl.py，以了解 ipywidget 切换按钮当前如何在工具之间切换。然后检查 notebook widget 集成中选择器的激活和绘制行为。完成标准是能够可靠地在缩放、矩形选择和套索选择之间切换，同时套索能够清晰地渲染并支持 notebook 选择。