Fix minor issues with funkis application

[patriksletmo]

Identified issues:

• [x] Race condition when applying. There is no check for whether a shift actually is available server-side.
• [x] Switch between red, yellow and green limit automatically depending on signups.
• [ ] It should not be possible to sign up as an orchestra fadder together with other funkis shifts.
• [ ] (Optional) Make it impossible to apply to two concurrent work shifts.
• [x] Comment away seed code for shifts to avoid shooting ourselves in the foot.
• [ ] Signing up for last shift in limit and then saving again will remove a user from the shift.

[ljukas]

Instead of commiting away seed code the seed code is disabled for production but enabled for test/development