#2312 - Add support for new external recommender v2

[jcklie]

What's in the PR

• [x] Move old external recommender to v1 subpackage
• [x] Can check connection to v2 recommender
• [x] Can select classifiers from the server
• [x] Predicting works
• [ ] Training works

How to test manually

• Check out https://github.com/inception-project/inception-external-recommender-v2
• Install with test dependencies pip install -e ".[all]"
• Run make inception_test
• Try setting up a v2 recommender using this service

Automatic testing

• [x] PR includes unit tests

Documentation

• [ ] PR updates documentation