Handle PYTHONPATH and the TimeTagger library

[HagaiHargil]

Since this is a Rust project we're kinda neglecting the Python side of things, and specifically the import of the TimeTagger library, which is obviously crucial. Even if we release the crate in a binary form, the call_timetagger.py file will remain excluded. Its first import part might have to be modified on a per-user basis due to the PATH modification done in it, so it's still unclear how to distribute it.

Perhaps we can embed its code in the Rust source code and ask users to have the TimeTagger library in their path beforehand.