Move distribution-based logic to config.py

[266-750Balloons]

As mentioned in #147, this moves anything that changes based on the distribution format of the picker to config.py to make it easier for porting to other distributions and increase maintainability. I have tested the commits in all 3 distribution formats, and there is no change to functionality.

Once again, thank you for your hard work on this project. It really feels like the least terrible emoji picker on Linux.