feat(components): add Form, FormGroup, FormItem, FormLabel

Supports #17

Fixes broken storybook.

TODO: Define stories using other components (e.g. NumberInput, Select...)

src/components/FormLabel/FormLabel.svelte

@@ -0,0 +1,14 @@
+<script>
+  let className = undefined;
+  export { className as class };
+  export let id = Math.random();
+  export let style = undefined;
+
+  import { cx } from '../../lib';
+
+  const _class = cx('--form-item', className);
+</script>
+
+<label for={id} class={_class} {style}>
+  <slot />
+</label>