Cannot build FusionDB Server when eXist-db public repo is offline

[adamretter]

Part of the build involves downloading eXist-db Apps from the eXist-db public repo for FusionDB's eXist-db compatibility component. Unfortunately when the eXist-db public repo is offline (which has been not infrequent recently), then the build fails.

We must remove this fragile dependency on the eXist-db public repo.