Optimize installed Python

[pasbi]

On windows, a whole python distribution is deployed.
The number of installed site packages can presumably be reduced significantly.
E.g., it is very unlikely that the omm-user will use pytest or unittest, they shouldn't be installed.
On the other hand, useful packages such as numpy could be included instead.

On non-windows platforms, the system python with all packages that are available, hence no optimization is required.

[pasbi]

many pycache directories are bundled currently, I presume they can be omitted as well.