Support for multiple warmup urls

[tagus]

Currently the warmup configuration only supports a single url that is queried to warm up the service. It would be nice if this was a list and edward queried the urls in order. This would allow us to exercise the service from multiple endpoints.

For a web server, a single url might not be enough to warm up static resources (js, sass). Currently, these resources would only be compiled upon visiting the specific pages where we often have to wait around while the page loads. With multiple warmup urls, we could compile all resources before ever accessing the service.