add stub. modalBody, modalHeader, modalFooter (#303)

src/lightning-stubs/modalBody/modalBody.html

@@ -0,0 +1,9 @@
+<!--
+Copyright (c) 2018, salesforce.com, inc.
+All rights reserved.
+SPDX-License-Identifier: MIT
+For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
+-->
+<template>
+    <slot></slot>
+</template>

src/lightning-stubs/modalBody/modalBody.js

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2018, salesforce.com, inc.
+ * All rights reserved.
+ * SPDX-License-Identifier: MIT
+ * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
+ */
+import { LightningElement } from 'lwc';
+
+export default class ModalBody extends LightningElement {}

src/lightning-stubs/modalFooter/modalFooter.html

@@ -0,0 +1,9 @@
+<!--
+Copyright (c) 2018, salesforce.com, inc.
+All rights reserved.
+SPDX-License-Identifier: MIT
+For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
+-->
+<template>
+    <slot></slot>
+</template>

src/lightning-stubs/modalFooter/modalFooter.js

@@ -0,0 +1,9 @@
+/*
+ * Copyright (c) 2018, salesforce.com, inc.
+ * All rights reserved.
+ * SPDX-License-Identifier: MIT
+ * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
+ */
+import { LightningElement } from 'lwc';
+
+export default class ModalFooter extends LightningElement {}

src/lightning-stubs/modalHeader/modalHeader.html

@@ -0,0 +1,7 @@
+<!--
+Copyright (c) 2018, salesforce.com, inc.
+All rights reserved.
+SPDX-License-Identifier: MIT
+For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
+-->
+<template></template>

src/lightning-stubs/modalHeader/modalHeader.js

@@ -0,0 +1,11 @@
+/*
+ * Copyright (c) 2018, salesforce.com, inc.
+ * All rights reserved.
+ * SPDX-License-Identifier: MIT
+ * For full license text, see the LICENSE file in the repo root or https://opensource.org/licenses/MIT
+ */
+import { LightningElement, api } from 'lwc';
+
+export default class ModalHeader extends LightningElement {
+    @api label;
+}