Add support for virtual envs when setting up development environment

[hemildesai]

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Currently, running make develop and make test installs python packages via the default system python (if a virtual env is not setup).

Ideally, there should be an optional step to setup and activate a venv.

Also, add files and folders to .gitignore from https://github.com/github/gitignore/blob/master/Python.gitignore

[hemildesai]

Happy to help with this.

[bfirsh]

@hemildesai That would be fantastic, thank you! This would avoid having to install the binary globally, too.