Update Slack report messages with API

[TimJentzsch]

Relevant issue: N/A

Description:

When a submission gets removed or approved via the API endpoints, the Slack report message is now updated accordingly.

Checklist:

• [x] Code Quality
• [x] Pep-8
• [x] Tests (if applicable)
• [x] Success Criteria Met
• [x] Inline Documentation
• [ ] Wiki Documentation (if applicable)