Enable stubbing all kinds of HTTP requests (not just XHR)

[shauvik]

Currently, cypress can only stub out XHRs but it would be great if it also did the same for static resources like js files.

In our case, we would like to stub a static js file URL that returns test content to check if our server-side code behaves well or fails in a reliable fashion if the js is an older/non-standard version.

[brian-mann]

We've laid the groundwork to now make this possible in 0.17.0. We need to now add the API's to control this behavior. It's on our radar.

[paulpruteanu]

Any update on this one?

[brian-mann]

Closing this in favor of this proposal which goes into a lot more detail: #687