feat(components): add Tile

Supports #34

TODO:

- remove exported props
- compose TileGroup, SelectableTile, RadioTile components

src/components/Tile/Tile.svelte

@@ -0,0 +1,14 @@
+<script>
+  let className = undefined;
+  export { className as class };
+  export let light = false;
+  export let props = {};
+
+  import { cx } from '../../lib';
+
+  $: _class = cx('--tile', light && '--tile--light', className);
+</script>
+
+<div class={_class} {...props}>
+  <slot />
+</div>