Range of `type` property

[evanp]

Issue #440 points out that the formerType property should match the same range as the type property. In formulating a possible change to the spec, there was disagreement on what the range of the type property should be. This issue will discuss that problem, separate from formerType.

[cristianolongoodhl]

As discussed in Issue #440 the value of formerType should be the same of the type property of the object before deletion, and the range of the type property is rdfs:Class. In this case, formerType should be an annotation property, for decidability reasons. Otherwise, I suggest to leave the formerType property range unspecified.