Add OSM and Strava Heatmap layers

[Matic K.]

Hello,

I'd like to suggest to add 2 new layer options to Mapy: OSM and Strava Heatmap.

OSM can be useful because it often displays extra details that may not visible in Mapy, for example.

Strava Heatmap is of course very useful to check which paths are more frequently visited than others.