Tweak student pay banner

[novoselt]

At the moment fresh student-pay project have two dismissable banners - one to pay the fee and one to get a license because the project is not upgraded. These are conflicting statements and the second suggestion is actually wrong - students should not get a standard license because they are required to get a course-specific one. So

1. Do NOT show the generic banner if "Pay the course fee" is shown.
2. Do NOT allow this banner to be dismissed - it is just one line, a non-threatening color, and since the students have to pay eventually, they might just as well to pay right away and enjoy proper experience.

[williamstein]

I asked one big user's opinion about "Do NOT allow this banner to be dismissed" and they are very much against this proposal: "As long as the banner comes back in if you refresh or re-open CoCalc, dismissing is probably okay. Space on the screen is pretty valuable! "