Add Current location button to map

Add a “Current location” button to the website map, similar to the one in the app, the one on Google Maps, etc.

User story: The user wants to browse crags in his/hers surroundings. The user does not want to see all crags on the globe and does not want to zoom in every time the map page loads.

Benefit: the page does not have to load and render all crags on the globe, which should mean less data transfer, memory and page load = many wins.