Removed deprecated code, unfreezed pymongo lib and Python 3.11 in Dockerfile

[1.7]

Added

• Integration test with MongoDB v7

Changed

• Moved tests and coverage from Travis to GitHub actions
• Updated python version and versions of some GitHub actions
• Unfreeze cyvcf2 lib to be able to install the software with Python>=3.8
• Installation instructions on README page to install mutacc using Python 3.8
• Unfreeze pymongo requirement and removed deprecated pymongo code to support latest version of MongoDB
• Updated pythin version to 3.11 in Dockerfile
• Updated MongoDB version to 7 in docker-compose.yml file

Fixed

• Badge on Readme page
• GitHub action to push the right image to Docker Hub
• Replaced deprecated pkg_resources lib with importlib_resources
• Path to app in tests_and_coverage.yml, coveralls step