Improve UX when submitting feedback

[murhum1]

Show a "feedback received" alert and hide the Submit button after submission to signal students that their feedback has been received and they can move on.

Why?

Student submission UX has been unclear, resulting in semi-accidental double submissions. See #122 for details. This should prevent these double submissions. Requires related A+ code to work (apluslms/a-plus#1505), so that jutut knows the exercise on A+ side has just received the "grading" result.

Fixes #122

Testing

What type of test did you run?

• Accessibility test using the WAVE extension.
• Django unit tests.
• Selenium tests.
• Other test. (Add a description below)
• Manual testing.

Did you test the changes in

• Chrome
• Firefox
• This pull request cannot be tested in the browser.

[ihalaij1]

I tried this and it works great!

I was thinking about hiding the "Submit" button. What if the student wants to edit their submission after submitting? They might not know that reloading the page brings back the "Submit" button and allows them to resubmit. @murhum1 @jsorva

Are we sure we want to hide the submit button in addition to showing the "Feedback received" alert?

[jsorva]

Thank you for looking into this!

The solution sounds mostly very good. But Jimmy’s point is valid, I think. Would it make sense to keep the button there, but to clear the input box (which I think doesn’t currently happen?) and perhaps change the text on the button a bit?

Apropos of this, to address the related issue #121, it might make sense to prevent the feedback from being sent if it’s otherwise identical from the previous one but the text box is empty.

[murhum1]

@ihalaij1 The students cannot edit a submission - if they click submit again, it will show up as a new comment on the same feedback thread. I was on the edge about removing the submit button though, I don't mind keeping it either for cases where students remember they wanted to add something.

I'll see if I can implement @jsorva's suggestion, or something alike, at least.

[ihalaij1]

Yeah, by "edit" I meant a student wanting to change their submission a bit and resubmit.

[ihalaij1]

I made some small changes to fix the margins, commit message, and brought back the Submit button.
You can continue from there @murhum1