Improve cohesion and code quality for Image Manager

[luciusyeo]

1. Reduce coupling and improve cohesion within the image folder.
2. LocalImages column is stored in the server (should remove)
3. Improve Logic: When any image (remote) is pulled from the server, extract filename from its uri, then check with SQLITE if the same filename (UUID) exist locally already. If so, then do not replace, but if dne, create that image locally.
4. Confirm the image cleanup logic for stale images.