Add option to support non-visual maps

See: https://github.com/Maps4HTML/HTML-Map-Element-UseCases-Requirements/issues/256 and 
 https://github.com/Maps4HTML/Web-Map-Custom-Element/issues/546

We should be able to control this via a maps setting / option.  Let's start with a simple option: on or off, and then if we like it we can refine, perhaps by domain.