Card icons were not using the correct padding

Thought about using $card-content-padding but that might leave room for error if it changes from one pixel value to four pixel values. Perhaps these should be four separate variables (e.g. $card-content-padding-top, $card-content-padding-left, etc.)
Merge pull request #958 from lonelyplanet/jd_fix_icon_padding

Card icons were not using the correct padding