Add option class passthrough for multi-select

[meuserj]

I had a fairly specific need to style a specific option tag differently than the rest of them in a multi-select box. This works somewhat similarly to the inherit_select_classes option, but it works on the option tags.

I've never worked with Coffee before, so I apologize if I have made any stupid mistakes. This code works for me, but the additional classes needs to be defined in CSS with the important rule if their style fields will be overwritten by search-choice.