UI cleanup

Cleaned up a bunch of the UI, including how items are positioned, how they look, and how the actual css is structured (in particular, embedding it all inside index.html was starting to get a bit unmanageable).

As part of attempting to make the look more consistent, I ended up changing a bunch of chat.js in order to make styling easier. In the process, I ended up adding "proper" fading, but killing client-side sorting. However, it doesn't seem like the sorting code did anything anyway, since the server will always deliver messages in the correct order (both channels and tcp guarantee in-order delivery). Maybe we'll want to add it back if we do client-side timestamping.

Another potentially controversial change is the movement of the shovel ("build menu") to the left, and the gun ("blast menu") to the right. I'm not sure if this is the right thing to do, and I was doing it mainly to experiment with the different emphasis it puts on the game, and to make it consistent with the name "buildblast". Thoughts?