Disposition without drag&drop

[lukasrad02]

Is your feature request related to a problem? Please describe.
Currently, disposition is only possible using drag&drop. This is cumbersome, especially on mobile devices or for shifts with a large number of participants.

Describe the solution you'd like
I don't have a clear vision of how the disposition view should look like, but have collected some ideas:

• Keep the layout as-is and keep drag&drop, but add buttons to each entry that move the entry to the respective box (e.g. ✅ for confirmed, ❔ for requested, ❌ for denied)
• Add checkboxes to each entry to allow moving multiple entries at the same time (using drag&drop or buttons above the boxes, similar to the events list page)
• Instead of a separate "Add others" box, add a "Add" button to each of the other boxes so that users can be directly added to the right category

Describe alternatives you've considered
see above

Additional context
none

[jeriox]

there are several other aspects regarding the layout of the disposition: #940 #1214 #243 #1346