Warn or error if VitessceConfig.__init__.schema_version is beyond that supported by the bundled JS package version

[keller-mark]

In https://github.com/vitessce/vitessce-python/blob/main/vitessce/_version.py specify a maximum schema_version value.

Perhaps warn in the constructor but error in the .widget() function? It is possible that a user just wants to construct a config and write to JSON, etc. without actually using the JS package/widget.