Cleanup pip install and fix readme example

[JasonMoho]

• Adds a step in GitHub actions workflow to test the pip install
• Adds fb15k end to end test based on the readme python example
• Updated readme python example to include preprocessing step
• Fix torch GIL issue when calling Trainer.train(). GIL needs to be released for any code which uses the autograd library
• Rename marius directory to marius_package, to avoid issues with python scripts in the root directory that import marius
• Test data cleanup
• Cleanup unnecessary .gitignore entries

Fixes #23