Small graphical update

Small update today that reworks all of the units to render as animated 2d sprites.

Based on how well this appears to have gone I am now considering reworking how I render the tile upgrades/modifiers (e.g. trees, villages, cactus' etc..) to also use billboards. We'll see..

I also modified the rendering of the actions list (the list on the left in-game showing the action history) to improve readability somewhat.

I have also added an action message at the end of each game turn to log the current weather state.