Allow http: url for custom basemap

[mnalis]

at https://geojson.io in Meta / Add raster tile layer one can enter URL for XYZ map.

However, if it is http:// and not https:// URL, it will fail with "Invalid tile URL. Must be HTTPS" error message.

My usage case is that I'm running mapproxy on my local machine, and mapproxy-util serve-develop mapproxy.yaml will only listen on http://localhost:8080/, not via https:

I can make it work, but it requires kludges in developer console to skip those https checks, after which it works fine (or I would need to setup whole web server, certificate infrastructure etc which is overkill).

It would be great if https://geojson.io could work out of the box with http: URLs. Thanks!