[Feature] Modular Cakes!

[AwkwardDryad]

Cake time!

Toppings:
 - fruit wedges
 - chocolate chips
 - cherries
 - strawberries
 - sprinkles
 - candles
 - OTHER CAKES

Frosting Styles:
 - classic
 - top swirls
 - bottom swirls
 - spirals
 - rose spirals

= You can light and blow out candles with disarm intent
= You can stack up to three cakes, transferring reagents, reagent capacity, and food buffs between them (up to 300u of reagent capacity)
= you can un-stack cakes with grab intent
= cake slices inherit the frosting styles and toppings of the cake that was sliced
= a few visual updates to the existing sprites for icing tubes and cake bases
= icing tubes now default to being whitelisted in the drink dispenser instead of the chem dispenser
= you may drink your frosting chems out of the icing tube

enjoy serving/murdering your customers in a very pretty fashion!



Pull Request: https://github.com/goonstation/goonstation-2020/pull/35

DMIs:
Icing (modifies food.dmi) - https://drive.google.com/open?id=1n7Q3kI...fy20_53hMI
Cake stuffs (modifies food_dessert.dmi) - https://drive.google.com/open?id=15Z9IMY...JSqmI4CeQ-