move links between works proposed changes

[tcouch]

I was looking for a way to remove the none-option from the select boxes and went down a bit of a rabbit hole. Anyway, I hope it's useful.

• Removes none-option from Work and Book select boxes when using form to update existing links
• Refactor the form's init method to hopefully make it a bit more readable
• Update disable checkbox js to disable definite book as well as def work checkboxes when Unknown Work selected