HID: apple: option to swap the 'Option' ("Alt") and 'Command' ("Flag") keys.

Use case: people who use both Apple and PC keyboards regularly, and desire to
keep&use their PC muscle memory.

A particular use case: an Apple compact external keyboard connected to a PC
laptop. (This use case can't be covered well by X.org key remappings etc.)

Signed-off-by: Nanno Langstraat <langstr@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>