Finish the Volunteer Manager MVP

Admin

[x] Add a card linking through to the upcoming event
[x] Enable entries on the logs page to be sorted
[x] Content management for global content
[x] Improve date and time formatting in the Logs page
[x] Migrate e-mail over to be an integration
- [x] Have an "outbox" with all messages that have been sent
- [x] Actually be able to send e-mail messages...

[x] Include publication status hotels and trainings on the dashboard
[x] Include the event's start date on the dashboard
[x] Include recent volunteer mutations on the dashboard (e.g. hotel rooms)
[x] Content management for each team
[x] Applications: Accept participation (+ generated e-mail)
- [x] Silent acceptation behind a permission
[x] Applications: Reject participation (+ generated e-mail)
- [x] Silent rejection behind a permission
[x] Applications: Ability to reconsider rejected applications
[x] Hotels: Overview of the hotel selection for volunteers
[x] Hotels: Assign volunteers to different hotel rooms
[x] Trainings: Overview of the training selection for volunteers
[x] Trainings: Assign volunteers to a particular training
[x] Volunteers: Cancel participation (+ generated e-mail)
- [x] Silent cancelation behind a permission
[x] Volunteers: Reinstate participation (+ generated e-mail)
- [x] Silent reinstatement behind a permission
[x] Volunteers: Display hotel preferences
[x] Volunteers: Display training preferences
[x] Volunteers: Enable their avatar to be changed
[x] Volunteers: Show volunteers who have cancelled

[x] Optimise the layout for dark mode
[x] Optimise the layout for mobile devices
[x] Training information should be fetched dynamically
[x] Add a placeholder button for sharing availability information
[x] Enable volunteers to share their hotel preferences
- [x] Confirm hotel information when an admin assigns the volunteer
[x] Enable volunteers to share their training preferences
- [x] Confirm training information when an admin assigns the volunteers