Add an intention to simplify negated expressions.

Given an expression of the form `!(a op b)`, replace it with `a !op b`.

From      | To
----------|----------
!(a in b) | a !in b 
!(a is b) | a !is b
!(a == b) | a != b
!(a != b) | a == b
!(a >= b) | a < b
!(a > b)  | a <= b
!(a <= b) | a > b
!(a < b)  | a >= b

Notes:
* This intention could probably be named better ("Push Not In" is awkward) but I can't think of a better (accurate) name.