Checklist for final Python publish of 3.0 support

[feuGeneA]

This issue is a checklist of items that need to be resolved or corrected before publishing finalized Python packages that support v3 of the protocol.

• Update release dates in all CHANGELOGs
• Publish docs and update doc links everywhere. For example, in contract_wrappers/src/index.rst, there are lots of references to https://0x.org/docs/contracts#..., which seem to be broken.
• Consider revising docker commands in documentation (docstrings) because they don't work as stated right now (because you need to specify the ganache version and snapshot name). Or skip that because it will "just work" later when we publish a stable v3 snapshot/docker-image?
• Consider revising example SRA URL in python-packages/sra_client/src/zero_ex/sra_client/__init__.py. Currently it points to https://api.radarrelay.com/0x/v3 (changed recently from .../v2). Does that even necessarily exist? Would it be better to use a 0x API URL instead?
• Remove --pre flag (which says "use pre-release versions") from all tox.ini files' run_tests_against_deployment targets.
• Remove v3-specific tags on docker image references, in both sra_client/test/relayer/docker-compose.yml and .circleci/config.yml, referring just to latest tags.
• Remove all setup.py version pins for python-packages/ interdependencies.