add new player_quality 'disabled' option

[raszpl]

fixes #2273

[ImprovedTube]

hi! @raszpl if auto equaled "do nothing", before and is now an option, then we need to migrate people from auto to disabled via background.js...?

[raszpl]

Yes, good point.

[raszpl]

but not like that :-)
all you need is delete player_quality when it was previously set to auto, player_quality_auto doesnt have to be touched, it already filters out Auto as that doesnt make sense for off focus setting.

all is needed here is

		chrome.storage.local.get('player_quality', function (result) {
			if (result.player_quality === 'auto') {
				chrome.storage.local.remove(['player_quality']);
			}
		});

[ImprovedTube]

player_quality_auto is a new key to tell if auto was removed once already.