Async loading of remote assets

[jthrilly]

As a final stage of remote asset implementation, we should support asynchronous loading of remote assets (primarily external data).

In Architect the user would be able to add a new asset or type "remote" (or similar). They would be able to construct a URL that would include templating for interview variable values (probably also a URL constructor worker that passes in the whole session/network model) like this: https://myuniversity.edu./myproject/?interviewID={egoID}

In Network Canvas we want to try to use new React features (suspense - mid 2019, and possibly concurrent mode - q2 2019) to implement this nicely. That means showing a spinner for loading data, and continuing to render everything else, and handling error states gracefully.