Graphical overhaul

Continuing the theme from the last update, this one replaces almost all of the existing models with some more modular ones.

This update also replaces all of the placeholder capsules for units and uses human characters, these are still not as I envision the final product but they're visually different enough to look better than previously.

Shoreline tiles should now run alongside a neighboring "solid" tile, and will even go as far as to bend around a single corner - I'm looking to improve this further as it can still cause some odd-looking maps if a single shore tile is surrounded on 3 or more sides.

Cactus' will no longer become trees in the desert if you perform the "milling" action on them.