Implement Blacklight::Allmaps Plugin

[mapninja]

As the manager of geospatial data holdings, I would like to be able to allow users to "georeference" scanned maps from our collections, while ensuring that the georeferenced derivatives (actually there aren't derivatives, but I'm not sure what else to call them) become discoverable.

Blacklight::Allmaps plugin is a new plugin for Blacklight/Geoblacklight, that provided iiif-native georeferencing capabilities for scanned maps exposed in blacklight/geoblacklight-based search portals using Allmaps.org georeferencing infrastucture

Repo: https://github.com/bplmaps/blacklight-allmaps

Dev Docs: https://github.com/bplmaps/blacklight-allmaps/blob/main/doc/development.md

Erik Larsen's Geo4LibCamp presentation: https://docs.google.com/presentation/d/1Pn81E1JS0CLn10lZWCpv-hwWcYYwtJkpxiiU6To61P0/edit?pli=1#slide=id.g2712a92aa67_0_50

Implementation Example: not-yet-georeferenced item: https://geo.btaa.org/catalog/p16022coll205:265 Georeferenced Item: https://geo.btaa.org/catalog/p16022coll230:4229