Refactor dynamic IIIF manifest generation so it mimics ddr-admin's logic &...
Refactor dynamic IIIF manifest generation so it mimics ddr-admin's logic & supports component-level manifests. Closes DDK-190.
- a component's manifest is just its parent item's manifest with a start property, to begin on the corresponding canvas
- image components now display the Mirador UI and a sidebar link to the manifest
- adds more tests and fixtures