Added custom cursors and window icon to Pixel.skin
Updated Window.CloseButton in Pixel.skin
Added road drawables to the DrawableLibrary, prepping for multiple road types.
Added basic HousingUpgradeSystem.
HousingUpgradeSystem now swaps in the BuildableComponent when upgrading.
Added exclusivity to systems that require a key binding to activate.
Now only a single one will be active at once, setting up for a bunch of city information/status screens.
Added Warehouse and StockpileComponent.
Added UI for managing Stockpiles.