Add information about the shift attendances targetted at the member office

[Theophile-Madet]

Member office people often don't know that excusing someone does give the excused person a shift credit. They also make mistakes often.
We could maybe add tooltips to all shift attendance buttons or a confirmation pop-up with some information about what that attendance state means.

[leonhandreke]

Yeah, more clarity here sounds like a good idea. Maybe we could have a "Missed" button that takes them to a page that has two selections:
a) No excuse – replacement shift plus makeup shift required
b) Excused – replacement shift required
c) Excused – no replacement shift required (in case of sickness, accident, etc.): [Reason field with hint text: Sick, accident...]

Adding a reason field might make it harder to just select this option without thinking too much.

[Theophile-Madet]

Solved in #597 and #607