Option to load individual test cases for USACO

[thecodingwizard]

Target use case: if a user gets a particular test case wrong after submitting, the user can then click on the test case to load that test case and get the input + expected output.

I forgot how big exactly all the USACO test files are, but I recall it wasn't very big at all. We could just write a script to download all the test cases and upload it to the server

[thecodingwizard]

we have all the test cases already (and a scraper for it too). shouldn't be too difficult to implement the rest I hope...