Using pybind_bazel and build wheels for Linux/macOS(Python 3.7, 3.8, 3.9)

[patrickhart]

Requiring a local virtual environment folder restricts platform independence and hinders building BARK for multiple Python versions. The majority of Python users now use Python 3.8 (https://www.jetbrains.com/lp/python-developers-survey-2020/) which BARK should be compatible for.

In this pull request:

• Using pybind_bazel avoids defining a local virtual python environment for building the python wrappings.
• Extended setup.py using Bazelisk making building BARK easy even without having installed Bazel
• Integrated GitHub Actions wheel builds that build BARK for Python3.7, 3.8, and 3.9 on Linux and macOS making it possible to easily use BARK using pip install bark-simulator
• wheels are only built and pushed when a git tag is pushed on the CI
• cleanup of the build structure; for some reason BARK required BARK itself as dependency; etc.
• removed manylinux CI build
• added MANIFEST.in to only include required files (reduces wheel size)
• generated wheels can be found here: https://pypi.org/project/bark-simulator/#files

Current problems not easily fixable:

• macOS runners reach rate limit on http request (error 403) on Bazelisk call. seems to be a more common problem. did not find a fix. results in arbitrary passing/failing of the macOS wheel builds