Add LiftRules.supplementalHeaders and deprecate supplimental variant.

supplementalHeaders is now a FactoryMaker, whereas supplimentalHeaders was a
volatile var containing a generation function, though it had recently been
switched to point to the listOfSupplimentalHeaders FactoryMaker.
Merge pull request #1533 from lift/spelling-bee

Spelling Bee: General spelling fixes + deprecations for 2.x series