Add indicator of context role for import and class registry UUID URNs

[mwatts15]

We currently automatically generate class registry and imports context URIs as UUID URNs. This is mostly fine except that it's not apparent what these URIs refer to without actually trying to resolve them, which makes debugging somewhat more difficult. URNs, generally, permit three optional components, one of which is called the "r-component" which can hold information for "resolvers" which includes owmeta_core. owmeta_core doesn't need this information to actually resolve the URI and indeed must not use this information over the configuration information from bundles and projects, but including something like "?+context_type=class_registry_context" would be very useful for debugging.