Clean up and fix requirements installation workflow

[pfaion]

This PR intends to clean up the dependency setup with the multiple requirements.txt files and fixes missing dependencies for Windows. This is a result of the discussion in #21

Relevant Changes

• No more requirements.txt files
• No more manual installation of glfw binaries, as pyglfw now ships with them. That means no more dependencies to setup! :tada:
• Correct automatic installation of source/wheel dependencies for Unix/Windows

Additional Notes

Since PEP508 all the required options can be handled via install_requires:

• install from GitHub
• install wheel from custom URL
• install differently based on OS

@papr @romanroibu can one of you test if this works on macOS? As in:

1. Make sure you don't have glfw installed in brew.
2. Create a clean virtualenv.
3. Just pip install . or pip install -e . from this repo.
4. Run pupil_invisible_monitor, make sure the app starts and you get an image from a PI.

• [X] I'll leave this as a draft for now. If it works, I'll adjust the related documentation as well in here and delete the requirements files.

[pfaion]

This is working on Windows with the glfw3.dll removed and on Linux with libglfw3 uninstalled from apt.

[papr]

Unfortunately, I do not have a 1+6 at home, but the installation went smoothly and the app starts correctly on macOS without brewed glfw.