Allow air gapped installation

[FranzForstmayr]

I would like to use pyapp to install my project on a air-gapped machine. Currently only the distribution can get embedded, but not the dependencies.

[trappitsch]

Tried this a while ago but not since as I didn't need it since. Did back then a quick write up for myself. Maybe this helps:

https://gist.github.com/trappitsch/c72a9ac067067abef705d77871225aab