Provide a template configuration entity to map rdf

[dannylamb]

Transferred from Islandora/documentation#486. Please see that issue for the original conversation.

Title (Goal)	RDF UI: Provide a template configuration entity to map rdf for additional modules
Primary Actor	Developer
Scope	architecture
Level	Medium
Story	As a developer, when I develop a custom module that would install custom bundles/fields/ontologies, I would like a systematic way to load and use custom ontologies, then define custom RDF mappings using these ontologies.

Examples:

• If using Islandora as an IR, have custom bundles/entity types like ETDs/journal articles/book chapters and use ontologies such as BIBO, COAR, and SPAR. In an ideal world, we would be using RDF UI to define a new content type like "ETD", configure a bunch of required fields that have human-friendly labels and descriptions, and map them to whatever ontologies we end up choosing (having dropdown menus for controlled vocabs would be rad too). Having the human-friendly labels on the new node creation form would allow us to use that form as a submission form as well, so students and faculty to self-deposit. Having non-RDF wizards create valid objects seems like a challenge, so having good UX will be very important.