[FEATURE] Customize Basemap and Config Example

[MatthewMuehlhauserNRCan]

Is there an existing issue for this?
No, this issue does not exist.

Who request this Feature
Myself

User Story
There doesn't appear to be a way to customize the available basemaps in geoview, either by adding or removing basemaps from the list. If this functionality does exist, it's not well documented and an example configuration should be created either way to show how to implement this properly.

It seems like the 09-package-basemap-custom navigator was created for this purpose, but never actually completed. There also appears to be some hints to custom basemaps in the code, but they don't seem connected to anything at the moment.

Implementation UI
No changes to UI needed, just an ability to configure the basemaps list.

Additional context
With the addition of vector tiles, also having a way to add a style URL to change how a basemap is presented could be an interesting option and could potentially be done easily enough by just updating the styleURL in the basemap list.