Improvements for mobile

I have updated the snowman graphic to include a more visible arrow indicator, scaled down a lot of the backgrounds and props, and removed the bilinear filtering on these items.

The performance on my phone seems better, and the angle indicator is much more visible now.

I hadn't originally intended for the game to be playable on mobile, but it has been fairly straightforward to add this in, I think mainly due to the extremely limited control scheme that I am using.

It will be interesting to see what kind of concessions I need to make for mobile devices when building more complex UI elements such as the in-game upgrade shop.