Detect hardware acceleration state

[becky-gilbert]

As part of handling #228 (green screen video recordings), it would be useful to know whether a participant's hardware acceleration is turned on or off in their browser settings. If it's possible for us to obtain this info from the browser, then we can:

• Alert the user and provide info on how to change this setting, since it can cause video recording failures (though we don't currently know if that's always the case - it could just be in some browsers/versions)
• Add the hardware acceleration state to the video meta data sent to lookit-api (Video upload metadata - document for future lookit-api#1025)

If it's not possible to obtain this info from the browser, then we should still consider adding a troubleshooting note about this to the video consent frame (NOT the video config frame, where the other troubleshooting notes are, because this particular issue doesn't happen when viewing the live camera feed - it only becomes apparent to the user when they try to play back a recording).