#259 Zoom to points (improve zoom factor)

[michael michaud]

Zooming to a point generally zooms to much (the user has no more no context and has to unzoom by several order of magnitudes to understand where he is).
The difficulty is that without a significant geometry envelope (point envelope has a null width and a null height), OpenJUMP does not know what an appropriate zoom level should be (it may be very different if the layer uses a projected or a geographic coordinate system).
With the help of some metadata (coordinate system, globale envelope of the layer, mean density of features), it would be possible to choose a better zoom level though.