Only allow shift signup a few hours in advance

[MichiK]

We are curently discussing how it might be possible to distribute access to popular shifts more fairly to angels without too much manual work involved. Currently, this could either be done by disabling self-signup and scheduling manually like the VOC does it or by creating shifts ad-hoc every day, which would increase workload on heaven during the event and is error-prone.

The signup_requires_arrival config option already is a nice idea as it requires people to show up in person but it still favors people showing up early on day -1 or so and allows them to block all the cool shifts for days.

So the idea came up to allow signup for shifts only a certain time in advance, e.g. 24 hours, or maybe even less for those shifts which will fill up within seconds after creation anyway (like bar shifts). This would ensure that popular shifts on later days will still be available for people arriving late and in addition, it would probably reduce freeloading due to people signing up for shifts early and then forgetting about them.

As a start, a global config uption similar to signup_requires_arrival would be nice, but having this configurable on a per-shift basis would be even better (with configurable defaults for rooms or shift types).

[msquare]

My ideas:

• Config per angeltype and/or per shifttype (leads to more complex shift state calculation since some angeltypes might be able to sign up earlier than others)
• Display countdown for signup on shift view
• Shift calendar filters free and full shifts. Is this still enough? Or do we need free+signup possible?
• Check the admin view - are admins able to signup everybody? An admin should not see the "not yet" state.
• If this feature is wanted, development and testing on own branch and test instance

[cbeneke]

It might also help to only allow up to 6 hours (or so) to be signed up to in advance. (E.g. the user is signed up for a shift t+0h until t+2h and one t+4h until t+8h; then the signup for future shifts will be blocked until t+2h and then allow another signup again)

Edit: As in do not disallow signup on general until t-x but depending on the workload of the angel

[MyIgel]

The global "Signup only x hours before" has already been implemented in #613