Refactor locations (version 2)

[skizzerz]

This is a significantly lighter refactor than #518. To wit,

• The absent status remains. We move people to the square or their house depending on their absent status at beginning of day, but otherwise location during daytime does not impact ability to vote by itself.
• Locations are singleton objects based on their name and do not carry any game state in the object itself. All game state is stored in GameState itself.
• There are no location subclasses; everything is just directly a Location.
• All access to location data is done via the locations APIs rather than directly modifying the GameState variables. This allows for easier future refactors of how we are storing data.