fix for chrome on android

[rwos]

apparently chrome on android implements the webcam api, so that works, except that it doesn't:

• somehow, it only captures one (extremely overexposed) frame, and (probably) errors out after that
• pressing space is a bit hard to do without a keyboard - we should trigger on touch/click of the live view canvas, too (or maybe add a button? not sure if it's possible to find out if the device has a keyboard)