Make crafting more robust

[Gjum]

• check if all items are in place before clicking the result slot
• check that cursor slot is non-empty after getting result, otherwise we did not craft
• speed up mass crafting with left+right clicking the grid slots
• should the crafting task return anything? maybe the slots with the crafting results?
• make Recipe a class, make the helpers in mcdata.recipes its methods
• get_any_recipe() should prefer small recipes if present

(taken from TODOs in the code)