Preserve current filter in URL

[stefanb]

Preserve all search parameters, including current map position & zoom in the URL hash.

Specifically:

• doctor type should be preserved in URL path, same as doctors card, eg /en/den-y, /sl/gp, /sl/gp-y
• other parameters (search, accepts) as either query string parameters or in hash
• map position in URL hash
  For this I am happy with https://github.com/mlevans/leaflet-hash but maybe something else from
  https://leafletjs.com/plugins.html#bookmarked-panzoom is better fitted for our case