Fixed NPE when accessing registry entries without environment.
Added example to @Doc
jsonhome-registry is now a library; an example registry web-app is created in jsonhome-examples/registry
Removed FileSystemRegistry, refactored jsonhome registry.
Refactored handling of different environments (now: registries)
Refactored resource format of registries
Added json-home document for registry example application.
Refactored repository resource structure