Add options for user and time filtering for `/search` command

[TimJentzsch]

Relevant issue: Closes #106.

Description:

This adds options to the /search command that allow to restrict the results to a specific user and time frame. The user executing the command will be the default user.

Screenshots:

Checklist:

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