Improve map loading performance

[Claudio-Chies]

One of the problems I experience on all devices is that the overview map loads quite slowly, especially while zooming and moving around. The underlying map is fairly fast, but the climbing areas layer seems to be a bottleneck. I saw a nice way of how this could be improved in the "Park4Night" App, whereby it doesn't load the layer with the location information while moving around and zooming, and only when you press "Search in this Area" it displays the location for the given map boundaries. This might be useful to reduce the server load and improve user experience, as currently the "Map:World" view starts from the global view, which means every user has to zoom in and move around quite a lot until the location his looking for is found.