Add Printed stabilizer

[jepler]

This new type of stabilizer works in conjunction with https://www.thingiverse.com/thing:4747414 -- Print that design's "StabilizerSlot_V2.stl" together with a 2U key using $stabilizer_type = "printed_stabilizer";. Push your bent 0.8mm diameter wire into the two retaining features before installing the key on the keyswitch.