Universal properties without funext, and localization

See <http://homotopytypetheory.org/2014/11/02/universal-properties-without-function-extensionality/> for a detailed description of the contents of this PR.
It could be redefined even if it were `Global`.  Do you mean "so redefining it doesn't leave us with the confusing state of having two `IsNull` aliases floating around, one shadowing the other", or do you mean something else?