Some APIs (e.g. Wikipedia) return 503 with lots of simultaneous requests

[ryanfb]

In loading the test page, a lot of the Wikipedia resources randomly show or don't show based on the Wikipedia API endpoint returning HTTP 503 (Service unavailable) randomly when a lot of requests are made at once.

There are a few different approaches that might help fix this:

• set cache to true with requests (and make sure we're actually using cache?) so that we don't request all resources on every page load if they're already in the cache
• make a per-service request buffer and request resources serially to avoid overload
• only make requests on link mouseover instead of requesting all resources on page load (though this may result in unacceptable delay?)
• make a request error handler that can retry requests after a (random, exponential backoff?) delay