Auto-mount volumes and auto-publish ports.

Changes

• Auto-mount volumes exposed from a container image.
• Auto-publish ports exposed from a container image.
• Remove run args support.
• Add a --docksi-dry-run flag to each image so as to see the volume and port mappings for an installed Docksi command before actually running it.
• Update README with instructions on all this.

Testing

• Built local Docksi image with these changes.
• Ran get-docksi.py (hacked to change image name) to install it.
• Ensured that docksi list still works.
• Installed another image (nginx) with docksi install.
• Ran the installed command to ensure it docker runs properly.
• Ran an installed Docksi command with --docksi-dry-run to display output like:

Volume flags: --volume /home/dan/.local/docksi-bin:/.local/docksi-bin 
Port flags: