feat(component): add ComposedModal

Closes #13

src/components/ComposedModal/ModalHeader.svelte

@@ -0,0 +1,43 @@
+<script>
+  let className = undefined;
+  export { className as class };
+  export let labelClass = undefined;
+  export let titleClass = undefined;
+  export let closeClass = undefined;
+  export let closeIconClass = undefined;
+  export let label = undefined;
+  export let title = '';
+  export let iconDescription = 'Close';
+  export let style = undefined;
+
+  import Close20 from 'carbon-icons-svelte/lib/Close20';
+  import { getContext } from 'svelte';
+  import { cx } from '../../lib';
+
+  const { closeModal } = getContext('ComposedModal');
+
+  const _class = cx('--modal-header', className);
+  const _labelClass = cx('--modal-header__label', '--type-delta', labelClass);
+  const _titleClass = cx('--modal-header__heading', '--type-beta', titleClass);
+  const _closeClass = cx('--modal-close', closeClass);
+  const _closeIconClass = cx('--modal-close__icon', closeIconClass);
+</script>
+
+<div class={_class} {style}>
+  {#if label}
+    <p class={_labelClass}>{label}</p>
+  {/if}
+  {#if title}
+    <p class={_titleClass}>{title}</p>
+  {/if}
+  <slot />
+  <button
+    type="button"
+    title={iconDescription}
+    aria-label={iconDescription}
+    class={_closeClass}
+    on:click
+    on:click={closeModal}>
+    <Close20 class={_closeIconClass} />
+  </button>
+</div>