Move app/src (mostly) to flipper-ui-core/src

Summary:
This diff moves all UI code from app/src to app/flipper-ui-core. That is now slightly too much (e.g. node deps are not removed yet), but from here it should be easier to move things out again, as I don't want this diff to be open for too long to avoid too much merge conflicts.

* But at least flipper-ui-core is Electron free :)
* Killed all cross module imports as well, as they where now even more in the way
* Some unit test needed some changes, most not too big (but emotion hashes got renumbered in the snapshots, feel free to ignore that)
* Found some files that were actually meaningless (tsconfig in plugins, WatchTools files, that start generating compile errors, removed those

Follow up work:
* make flipper-ui-core configurable, and wire up flipper-server-core in Electron instead of here
* remove node deps (aigoncharov)
* figure out correct place to load GKs, plugins, make intern requests etc., and move to the correct module
* clean up deps

Reviewed By: aigoncharov

Differential Revision: D32427722

fbshipit-source-id: 14fe92e1ceb15b9dcf7bece367c8ab92df927a70

desktop/flipper-ui-core/src/ui/components/ToolbarIcon.tsx

@@ -0,0 +1,49 @@
+/**
+ * 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 Glyph from './Glyph';
+import Tooltip from './Tooltip';
+import {colors} from './colors';
+import styled from '@emotion/styled';
+import React from 'react';
+import {Tracked} from 'flipper-plugin';
+
+type Props = React.ComponentProps<typeof ToolbarIconContainer> & {
+  active?: boolean;
+  icon: string;
+  title: string;
+  onClick: () => void;
+};
+
+const ToolbarIconContainer = styled.div({
+  marginRight: 9,
+  marginTop: -3,
+  marginLeft: 4,
+  position: 'relative', // for settings popover positioning
+});
+
+export default function ToolbarIcon({active, icon, title, ...props}: Props) {
+  return (
+    <Tooltip title={title}>
+      <Tracked action={title}>
+        <ToolbarIconContainer {...props}>
+          <Glyph
+            name={icon}
+            size={16}
+            color={
+              active
+                ? colors.macOSTitleBarIconSelected
+                : colors.macOSTitleBarIconActive
+            }
+          />
+        </ToolbarIconContainer>
+      </Tracked>
+    </Tooltip>
+  );
+}