Improve card code, support MacOS

[petabyt]

On the MacOS/Linux side of things, this script inspires most of what MLinstall currently does: https://github.com/reticulatedpines/magiclantern_simplified/blob/dev/tools/make-bootable/make_bootable.sh

• Show more information on the card, such as capacity. Signal to the user that it actually detects the card.
• Indicate what flags are already written on the card.
• Support multiple cards. Don't just use the first device named EOS_DIGITAL.
• Support MacOS. This is really not that hard but I don't have a Mac to test with.