Updating Dockerfile and correcting bugs

[jagalindo]

This PR resolves issue #25. This Includes the following changes:

• Fixing a python version and base distribution to avoid problems with dependencies in the future.
• Installing mupdf from the sources so we can rely on the proper pymupdf version
• Adding a precompiled image hosted in dockerhub to avoid time on compiling this.
• Updating mupdf to 1.18.0