As a user, I would like to manually tag faces in my pictures in case they were not automatically detected.

Related Issues / PRs:

• People: Allow users to manually tag faces #5081

Acceptance Criteria:

• There MUST be an option to display all markers (automatically created and manual) in fullscreen mode
• The user MUST be able to mark a face (ideally using a square) in fullscreen mode
• The user SHOULD be able to assign a person to face markers in fullscreen mode
• The face marker MUST be saved in the database
• Manually marked faces MUST appear on the people tab within the edit dialogue
• The UI MUST be fully responsive
• Unit tests for the core functionality MUST exist
• Acceptance for the core functionality MUST exist
• Documentation MUST be updated