Clean up branches and code

[pollytur]

• We have several outdated branches, which should be cleaned.
• We also need to remove non-used datasets (e.g. Mouse2pStaticImageDataset, Mouse2pVideoDataset)
• Clean up dependencies (eg plotly, hydra -> replace with a simpler yaml parser)
• Add support for json files (and not only yaml ones)

And add some documentation (maybe with mkdocs / sphinx)

[reneburghardt]

Tom added documentation via sphinx in here: #62
See also readthedocs-website (although currently not up-to-date): https://experanto.readthedocs.io/en/latest/

[pollytur]

Old branches are cleaned up and non-used datasets are removed in #79

[pollytur]

• support for json files and separation of configs is still needed
• removing unnecessary dependencies is still needed as well