Added poetry dependency management, updated dockerfile

[d3an]

• Added poetry dependency manager
• Removed unused django-rest-framework alias dependency
• Updated Dockerfile to reflect the change.

@CalderLund test it locally before you merge. The Dockerfile build passed on my end.

[CalderLund]

Does not work with docker-compose up --build.

web_1  |   File "manage.py", line 16
web_1  |     ) from exc
web_1  |          ^
web_1  | SyntaxError: invalid syntax

I think it is trying to use python 2.7, but I'm not sure.