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

.github/workflows/ci-testing.yml

@@ -25,6 +25,7 @@ jobs:
       if: matrix.requires == 'minimal'
       run: |
         python -c "req = open('requirements.txt').read().replace('>', '=') ; open('requirements.txt', 'w').write(req)"
+        python -c "req = open('requirements-extra.txt').read().replace('>', '=') ; open('requirements-extra.txt', 'w').write(req)"
 
     - name: Cache pip
       uses: actions/cache@v1