Improve bounding box for route

[karussell]

There are several things we can improve:

• If we have a very short route it is zoomed to it even if overview is lost. I.e. we need a minimum bbox (or minium zoom parameter?).
• Additionally ensure that the markers are inside this bbox. https://graphhopper.com/maps2/?point=51.393745872521635,14.263346645918233&point=51.389093074131665,14.27498616022396&vehicle=car
• Additionally we have a flickering for the initial map as we first set the default center and zoom and then set the route (or /info) bounding box. We could avoid this instead of calling fitBounds initially when we calculate zoom+center from bounding box or use add initial bounds as map constructor option #1970 mapbox/mapbox-gl-js#5518 see avoid initial fitBounds #71
• the map is zoomed out too much (world is visible twice)

[Janekdererste]

The bounding box should have a minimum size and it should always include the markers

[easbar]

Another problem is that the elevation widget might cover one of the query points, for example here:

https://graphhopper.com/maps2/?point=48.118447%2C11.539497&point=51.442113%2C14.265179&profile=car

So we should probably only take into account the available vertical space above the widget, and only use the entire vertical space when the widget is closed.