recipe icon names must match the recipe's 'type' field, but in all lowercase
there must be one recipe icon twice the width of the actual icon, and contain the UP state in the left half, and the OVER state in the right half, each state should be 18x18 pixels
total recipe icon size must be 36x18 pixels (they will be resized)
recipe icons must be png files or they will not load correctly
recipe icons should be cropped pixel-close