Switch to using the contextual config everywhere

api/auth.go

api/custom/exports.go

api/custom/imports.go

api/custom/quarantine.go

api/r0/identicon.go

api/r0/preview_url.go

api/r0/public_config.go

api/r0/thumbnail.go

api/r0/upload.go

cmd/media_repo/inits.go

controllers/data_controller/export_controller.go

controllers/data_controller/import_controller.go

controllers/download_controller/download_controller.go

controllers/download_controller/download_resource_handler.go

controllers/preview_controller/acl/acl.go

controllers/preview_controller/preview_resource_handler.go

...ers/preview_controller/previewers/calculated_previewer.go

controllers/preview_controller/previewers/http.go

...lers/preview_controller/previewers/opengraph_previewer.go

controllers/quarantine_controller/quarantine_controller.go