separate requirements for logger dependencies (#792)

* added file that contains information on the minimal versions needed for the supported loggers

* copied minimal version, combined files, deleted duplicates

* sorted functions in tests/test_loggers.py to be consistent

* expanded wandb logging test; added minimal versions for requirements-extra.txt; increased the amount of training data that is used for tests

* formatting

* added requirements-extra.txt to MANIFEST.in

* reverted wandb test; ensured minimal version for dependencies in requirements-extra.txt in ci-testing.yml