"Submit your system" buttons are not 100% intuitive

[neubig]

The front page is greatly improved! I looked at it from the point of view of a person who was using the page for the first time, and I wanted to figure out how to submit a system.

• I clicked the "submit a system online" button, and it sent me to the systems page. But:
  • I wasn't able to submit because I wasn't logged in. We probably need to add "sign up" and "sign in" before the "submit" buttons, and gray them out if the person is not signed in.
  • I didn't know what to do on the systems page, I see lots of systems but it's not clear how to submit. It'd be nice if the system submission drawer was automatically opened.
• I clicked the "submit a system via API"
  • This is a bit better, but it suddenly sends you to a github page which is a little bit jarring. Maybe we could change it to "Install client and submit via API (github)." or something.