Add option for switching between different rear cameras

[odin-h]

Problem

Some phones come with more than one rear camera and the default camera selected by html5-qrcode is not always the best option. For my phone it always selects the wide-angle lens which is really bad for scanning barcodes.

Proposed solution

Add a button or dropdown for switching between available cameras or avoid defaulting to wide-angle lenses.

Additional context

Mockups

Part of

• #473