Implement Traversable/Foldable-Burning-Bridges Proposal

More details to follow. I've created this ticket to be able to refer to from related preparatory commits.

In a nutshell the FTP (Foldable/Traversable-Proposal) sub-goal of the BBP (Burning-Bridges-Proposal) includes to be able to compile code like the following w/o errors (due to conflicting definitions):

module XPrelude (module X) where

import Data.Foldable     as X
import Data.Traversable  as X
import Data.List         as X
import Control.Monad     as X
import Prelude           as X

Other goals include to generalise/weaken type-signatures where possible w/o breaking (much) compatibility with existing code. An in-depth design-document is in the works.