A few set lemmas from CakeML.
Added CakeML list theorems to listScript.sml

Added a new function, nub, which removes all duplicates.

I'm not sure how to decide what goes in list and in rich_list, so I put
everything in list that I could. That is, everything but theorems about
rich_list only constants and theorems whose proofs depend on rich_list
theorems.
More CakeML theorems about lists

The ones that couldn't go into listTheory