Downloading from external source should be supported

[BlackVegetable]

Rather than relying on a filepath for a local resource, both the run-time and the edit-time paths should be allowed to be remove paths. Due to other issues which address improving the edit-time setup, this issue could be satisfied by only changing the run-time functionality. Specifically, it would be simple to add another populate-at-runtime style function named populate-at-runtime-remote that expected a remote path to a server and file and performed the download before doing exactly what populate-at-runtime does.

[BlackVegetable]

Issue pending on url-regexp being made part of the public API. There is a pull request in the works for the Racket language, but if it takes too long, I'll throw together my own regex for the short term, and open an issue to replace my regex with url-regexp when it is public.