MonadBase instance for FT and MonadBaseControl instances for FreeT and FT

[duog]

These MonadTransControl/MonadBaseControl instances require the freed functor to have a Traversable instance. A proof of the MonadTransControl laws is supplied as a comment with the instance for FreeT.

The additional dependency of monad-control is added, which brings in no more transitive dependencies.

[treeowl]

Is this possible for CofreeT too? That could be rather useful.