Fix and Improve Absence

[MineKing9534]

Checklist

• [x] Read Contribution Guidelines and Style Guides
• [x] Test the Code
• [x] This PR is ready to review and merge

Description

• Fixes issues with the current features
• Now integrates with staff message
• Now integrates with meeting absences

Database Migration

Because of heavy changes to the internal structure, it is recommended to let the bot recreate the table. This also means, that all currently absent staff members will have to run the command again.

drop table absences;