Add historical map archive davidrumsey.com

[stefan123t]

Appreciate your work on glueing together map services. Would you mind taking a look at davidrumsey.com to check out whether it is feasible to add their vast collection of historical maps into MapSwitcher. Note that some of their maps have been geolocated and overlayed to current WMS too.

See here for a map of their georeferenced maps: https://www.davidrumsey.com/view/georeferenced-maps