Depend on psycopg2-binary instead of psycopg2.

[torotil]

This makes it possible to install the Python venv without the need to compile anything.

fixes #323

[dracos]

I understand why this would be nice for development/ease of setup; however psycopg2 says, at https://www.psycopg.org/docs/install.html#install-from-source "If you are the maintainer of a published package depending on psycopg2 you shouldn’t use ‘psycopg2-binary’ as a module dependency. For production use you are advised to use the source distribution."
If a user of mapit wishes to use psycopg2-binary they can of course specify it themselves in their requirements and it will be used.

[torotil]

Thanks I didn’t know that. Is there a way of specifying it only as dev-dependency then?

[dracos]

Python packaging, as far as I know, does not have such a concept. If you wish to use the binary package, you can install it in your venv first, manually, or (I guess) by specifying it first in your own requirements.txt

Looking at psycopg/psycopg2#674, I don't want to get involved with that :)