Add experiment tracking using mlflow

[wouterjdb]

This PR adds the possibility to run multiple flownet configuration files and do experiment tracking using mlflow.

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Contributor checklist

• 🎉 This PR closes Tracking of flownet runs #232, DeprecationWarning: Specifying whether element are required directly is deprecated #233
• 📜 I have broken down my PR into the following tasks:
  • Add mlflow dependency
  • Add hyperopt dependency
    • Expose choice between random search and optimization
  • Add hyperparamter running mode in arg parse
  • Parse configuration file with ranges and choices
    • Initial parsing
    • Add flexibility for user
  • Generate mlflow experiment
    • Run flownet
    • Generate metrics and store in mlflow
• 🤖 I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR.
• 📖 I have considered adding a new entry in CHANGELOG.md.
• 📚 I have considered updating the documentation.

[wouterjdb]

Tested now with the Egg CI Model. The workflow is working using hyperopt and visualization/tracking with MLFlow:

I track however a metric of "1" at the moment. Still a todo. Let's look at this tomorrow @edubarrosTNO.

[wouterjdb]

Added metrics and parameters. Exposed hyperopt options in config.

[olelod]

Nice work. LGTM.