Make pip installable

[oriordanemily]

Following these instructions https://packaging.python.org/en/latest/tutorials/packaging-projects/

[oriordanemily]

First version of this it to make things locally installable, which was done with this commit:
84097c8

Instructions were added to the README on how to install locally with this commit:
b32a4c6

Will leave this issue open until we upload to PyPI, but this may be a little while yet while we continue developing and polishing the repo.

[oriordanemily]

Note to self: the pip install -e . command will soon be deprecated when used with a setup.py file (see pypa/pip#11457)
This is being considered on the branch toml_pip_installation, need to chat with Lexi about it.
Look at https://medium.com/@codebyteexplorer/build-your-first-python-package-with-pyproject-toml-19e2119edbca for further help.

[oriordanemily]

a64b7f7

This commit has deleted the setup.py file and created a pyproject.toml file. Seems to be working (although required me to conda install pipinto my new environment before running pip install -e ., which I don't think I had to do when I had the setup.py file).

[oriordanemily]

As an update: I will do this once we have a first 'stable' version of Duplexity up and running. I also want us to look into versioning the package before we do this.