Add watchstatus Slack command

[TimJentzsch]

Relevant issue: Closes #363

Description:

Adds a new watchstatus Slack command, which will display the current check percentage for the given user.

Checklist:

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