Game world and scenery

We are mostly done with the UI elements, so we can now go into the game scenery components. We will have some new components to do--the player castles, a health and food bubble for each one, and some animated clouds in the background for good measure.

Create a new world.js file in the components folder, and include it in the page:

<!-- ... -->
<script src="components/ui.js"></script>
<script src="components/world.js"></script>
<script src="main.js"></script>

We will start with the castles.