Deal with non-CORS URLs

[gavinr]

If the url is not sending a CORS: * header, then we cannot map it. Maybe think about using a public proxy for these urls or some other solution.

At least give an error explaining the situation.

[acdpsn]

Can I work on this? It sounds simple enough to just implement an error popup.

[gavinr]

@akim8 yes that would be great - basically if a URL that does not have a cors header is used, we should show at the very minimum a modal popup explaining the situation. Thanks!