Utility function to convert population checkpoint into pandas dataframe.

- Implement utility function to convert pickled population checkpoints into a pandas dataframe containing a list of all individuals and their attributes as a table.
- Implement basic plot function "loss vs. generation / runtime", color / marker style according to rank / island.
- Provide basic analysis script to be executed in a folder containing checkpoints..
- Future: (Customizable) hooks upon specific events in the `Propulator`'s `_work` function to observe the optimization process on the fly while it is running, e.g., with TensorBoard.