Adds Undershirts [Merge dis]

Sprites by MrSnapwalk mainly

They are in the Preview
They are in Game
They are in your save files
They are changeable via clicking on a Dresser
They make you sexy, too sexy for your shirt, so sexy it hurts.

(Yes I know I said I'd port the bay ones but they're really really different to how we do things, so coded from scratch)