Yarn workspaces

Summary:
1) moved "sonar/desktop/src" to "sonar/desktop/app/src", so "app" is now a separate package containing the core Flipper app code
2) Configured yarn workspaces with the root in "sonar/desktop": app, static, pkg, doctor, headless-tests. Plugins are not included for now, I plan to do this later.

Reviewed By: jknoxville

Differential Revision: D20535782

fbshipit-source-id: 600b2301960f37c7d72166e0d04eba462bec9fc1

desktop/app/src/ui/components/Toolbar.tsx

@@ -0,0 +1,45 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {colors} from './colors';
+import FlexRow from './FlexRow';
+import FlexBox from './FlexBox';
+import styled from '@emotion/styled';
+
+/**
+ * A toolbar.
+ */
+const Toolbar = styled(FlexRow)<{
+  position?: 'bottom' | 'top';
+  compact?: boolean;
+}>(props => ({
+  backgroundColor: colors.light02,
+  borderBottom:
+    props.position === 'bottom'
+      ? 'none'
+      : `1px solid ${colors.sectionHeaderBorder}`,
+  borderTop:
+    props.position === 'bottom'
+      ? `1px solid ${colors.sectionHeaderBorder}`
+      : 'none',
+  flexShrink: 0,
+  height: props.compact ? 28 : 42,
+  lineHeight: '32px',
+  alignItems: 'center',
+  padding: 6,
+  width: '100%',
+}));
+Toolbar.displayName = 'Toolbar';
+
+export const Spacer = styled(FlexBox)({
+  flexGrow: 1,
+});
+Spacer.displayName = 'Spacer';
+
+export default Toolbar;