Implement lat/lon data-referenced annotations on geo and mapbox subplots

If annotating a point in a scattergeo plot, we should be able to refer to the co-ordinate of the point we must refer to in terms of "lat,lon". In fact, the annotation is required to be "x,y".
This is quite problematic: even when using a conversion factor as below, because when the map is zoomed, the annotations don't remain attached to the plot. We should be able to annotate "the lat-lon point that is associated with the marker", rather than "the x-y point on the screen".

annotation = {
text: "my_annotation",
x: (data.points[i].lon + 180)/360,
y: (data.points[i].lat/200) + 0.5 //yes, 200 not 180.
}

首先，使用 issue 中的 lat/lon 示例，在 scattergeo 或 mapbox subplot 中复现注释行为。跟踪缩放期间注释如何相对于地理坐标进行定位，并在注释能够指向一个地理点且缩放后仍附着于该点时，视为工作完成。