Show constant warning to applicant if availability is zero

[jonatanschroeder]

We have a few applicants that have set their availability to zero by mistake. I want to make sure that, if they do that, they understand what this means. The warning should be shown on the top in a fixed position. Also, the "Submit" button could be changed to something like "Confirm unavailability", with a tooltip that mentions an availability of zero.

[jonatanschroeder]

Please change the availability field to be a select, with the options:

• 0 (not available)
• 1 quarter load (0.25 load, 33.75 hours)
• 2 quarter loads (0.5 load, 67.5 hours)
• 3 quarter loads (0.75 load, 101.25 hours)
• 4 quarter loads (full load, 135 hours)

[kukuminer]

Completed. Let me know if you want any kind of additional helper text like there was before

[kukuminer]

resolved by #151