Trying to regrade/download/excuse/delete over 200 submissions turns into a bad request

[coder6583]

Your environment
Newest Autolab branch

Steps To Reproduce

1. Select over 200 submissions
2. Try to regrade/download/excuse/delete

Current behavior
Goes to a bad request page

Expected behavior
Successfully execute the regrade/download/excuse/delete

This issue is related to PR#2248. Because the regrade all button is gone, we are currently putting all of the submission IDs into the url of the regrade/download/excuse/delete request. For example:

Because the url is so long, it is turning into a bad request. A possible fix is splitting the requests up, or putting the ids into the body of the request.

[KesterTan]

Create submissions still capped at 300 users