Push a django success message on a successful form submission, because otherwise the result is unclear

[viktor-yunenko]

When a form is added eg at the bottom of the page, the page is reloaded but the user doesn't seen anything. They might intuitively think that something went wrong, then they would scroll all the way down and only then notice that the form disappeared, and after looking for it they might notice the plaintext success message, or might miss it.

We can reduce the potential confusion by using the messages framework.

[viktor-yunenko]

I noticed that there's a success message, but it appears only after the user manually reloads the page one more time?

[viktor-yunenko]

I disabled that django message because it has always been appearing on a random page.