Make the SDF "back" option a global setting for the deck.yaml file, and add "top" as one as well

[sharkbruhaha]

The card deck "top" setting is only available when using the upload files option of making a deck, NOT in the actual deck.yaml that is documented. Can we please get this added, and set as a top level/global setting:
(updated sdfv to .7 for example of the update to the format)
`
top: deck_top.png
back: deck_back.png
name: 2C
sdfv: 0.7
img: 2C.png
data:
value: 2
suit: Clubs

name: 3C
sdfv: 0.7
img: 3C.png
data:
value: 3
suit: Clubs
`