Add loading indicator

[kevinsimper]

When I open the map up with this https://tyrasd.github.io/latest-changes/#14/55.6848/12.5723

The data takes 10 seconds to load

[kevinsimper]

Was adding in @rene78 version
rene78@011df56

[rene78]

I guess overpass has something like a waiting queue, which leads to longer loading times of latest-changes.