Migrate to GHA, refactor CLI, & fix bugs

• Move continuous integration for testing and deployment to Github actions
• Refactor the command line interface and add the yggdrasil [subcommand] CLI with subcommands for other command line actions so that the CLI can be called with a specific version of Python via python -m yggdrasil [subcommand]
• Fix bug where colons cause environment variables to be invalid for R models run in Conda environments on Ubuntu
• Update the conda recipe so that the yggdrasil configuration file and R package are removed on uninstall