DevTools: Add shortcut keys for standalone version

Suggested keys:
* ⌘1 - Switch to "Components" tab
* ⌘2 - Switch to "Profiler" tab

Note that these shortcut keys should **only** be implemented for the [standalone DevTools](https://www.npmjs.com/package/react-devtools) since (1) the browser already uses these shortcut keys and (2) the "Component" and "Profiler" tabs are only part of DevTools in the standalone version anyway.