feat(component): add ComposedModal

Closes #13

src/components/ComposedModal/ModalFooter.svelte

@@ -0,0 +1,37 @@
+<script>
+  let className = undefined;
+  export { className as class };
+  export let primaryClass = undefined;
+  export let primaryButtonText = '';
+  export let primaryButtonDisabled = false;
+  export let secondaryClass = undefined;
+  export let secondaryButtonText = '';
+  export let danger = false;
+  export let style = undefined;
+
+  import { createEventDispatcher, getContext } from 'svelte';
+  import { cx } from '../../lib';
+  import Button from '../Button';
+
+  const dispatch = createEventDispatcher();
+  const { closeModal, submit } = getContext('ComposedModal');
+  const _footerClass = cx('--modal-footer', className);
+</script>
+
+<div class={_footerClass} {style}>
+  {#if secondaryButtonText}
+    <Button kind="secondary" class={secondaryClass} on:click={closeModal}>
+      {secondaryButtonText}
+    </Button>
+  {/if}
+  {#if primaryButtonText}
+    <Button
+      class={primaryClass}
+      kind={danger ? 'danger' : 'primary'}
+      disabled={primaryButtonDisabled}
+      on:click={submit}>
+      {primaryButtonText}
+    </Button>
+  {/if}
+  <slot />
+</div>