Added the Package class to GoodGet, representing a package we've got (including it's version and when we got it).
Added the IGot interface, exposing the methods used by GoodGet to query what packages we got as well as to store information about new packages retrieved.
Added IGot reference as a dependency injection entrypoint for the GoodGet module itself.
Added GotNone implementation of IGot, always returning no packages are installed whatsoever.