Add methods to the presenter which expose information about the deprecation of the set

I was a bit unsure about adding the two new fixtures specs `DeprecatedSpec` and `DeprecatedInFavorOfSpec`, but I wanted to have test cases covering those code paths. Maybe there is a better way to do it?

These changes are preparations for a PR that implements CocoaPods/CocoaPods#2180
We use [Rubocop](https://github.com/bbatsov/rubocop) with custom settings which you can see in the root. Style violations make the guide fail but this wasn't catch.