Implement core layout component BaseLayout

This is the default layout of Nord Docs that consists of the `Root` core
container (1) as root element and the core components representing the
header (2), the main page container (3) and the footer.

References:
  (1) #36
  (2) #64
  (3) #65

Associated epic: GH-63
Depends on GH-65
Relates to: GH-36, GH-64
GH-66

src/components/layouts/core/BaseLayout/BaseLayout.jsx

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2018-present Arctic Ice Studio <[email protected]>
+ * Copyright (C) 2018-present Sven Greb <[email protected]>
+ *
+ * Project:    Nord Docs
+ * Repository: https://github.com/arcticicestudio/nord-docs
+ * License:    MIT
+ */
+
+import React, { Fragment } from "react";
+import PropTypes from "prop-types";
+
+import Page from "containers/core/Page";
+import Root from "containers/core/Root";
+
+/**
+ * The base page layout providing the main container that wraps the content.
+ *
+ * @since 0.3.0
+ */
+const BaseLayout = ({ children }) => (
+  <Root>
+    <Fragment>
+      <Page>{children}</Page>
+    </Fragment>
+  </Root>
+);
+
+BaseLayout.propTypes = {
+  children: PropTypes.node.isRequired
+};
+
+export default BaseLayout;

src/components/layouts/core/BaseLayout/index.js

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+export { default } from "./BaseLayout";

test/components/layouts/core/BaseLayout/BaseLayout.test.jsx

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+/*
+ * Copyright (C) 2018-present Arctic Ice Studio <[email protected]>
+ * Copyright (C) 2018-present Sven Greb <[email protected]>
+ *
+ * Project:    Nord Docs
+ * Repository: https://github.com/arcticicestudio/nord-docs
+ * License:    MIT
+ */
+
+import React, { Fragment } from "react";
+import { render } from "react-testing-library";
+
+import BaseLayout from "layouts/core/BaseLayout";
+
+test("snapshot", () => {
+  const { container } = render(
+    <BaseLayout>
+      <Fragment />
+    </BaseLayout>
+  );
+  expect(container).toMatchSnapshot();
+});

test/components/layouts/core/BaseLayout/__snapshots__/BaseLayout.test.jsx.snap

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+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`snapshot 1`] = `
+<div>
+  <main
+    class="sc-bdVaJa eYFyfX"
+  />
+</div>
+`;