Fix getProgramPath() to find Python module in virtual environment on Windows and Linux

[lukashof]

There are various instances where data like scene or geometry files is loaded and getProgramPath() is used to find the right folder. However, when using the Python bindings from a virtual environment using the built-in venv-Module this won't work, since the method returns the path to the global Python interpreter. The only (very crude) workaround I have previously found was to place the relevant data in the global interpreter, which is not ideal and requires admin-privileges.

This PR contains a modification to find the correct Path of the venv, if the python bindings are used. I realize the implementation is a bit simplistic and depends on the found executable's name, and might therefore not cover all available Python distributions.

I made no changes to the Apple implementation, since I don't have a machine available to test this on.

I have previously discussed this with @digitalillusions in #283, where he mentioned that the issue does not occur with Anaconda. I tested my solution with Anaconda on Windows as well and had no issues.

This might solve the problems from discussion #151 and #254, although the latter one was already closed.

Looking forward to any feedback!

[lukashof]

I was never happy with the solution I proposed. I just rebased it to the latest version. In doing so, I found that I couldn't compile via the setup.py anymore because pybind wouldn't find my Python installation in a non-standard directory on Windows. I've added a commit to address this.

I've also reworked the original solution to the program not finding the module correctly. It now identifies whether it runs in Python from a mismatch between the executable and module. The correct directory is also found by looking for the data and resources folders.

So far, I only tested the Windows version with venv. I'll test on Linux too. Unfortunately, I don't have access to a Mac. I can only trust my LLM of choice for that bit.