React 16 changes the default error behaviour such that an error in any components now unmounts back to nearest error boundary. If there are no error boundaries (the current state in Riot, since this a new feature of React 16), then React unmounts the entire app leaving a blank screen, such as in #10983.

We should at least add a very basic error boundary for the whole app with:

• "Something went wrong!" text
• "Submit debug logs" button to rageshake
• Ensure update checking is functional (to receive fixes)

We could build on this in future to add more specific boundaries for e.g. single room's view or something.