VS: Rename VS 14 generator to 'Visual Studio 14 2015'

Now that we know the year component of this VS version we
can add it to the generator name.  For convenience, map
the name without the year to the name with the year.
Merge topic 'vs14-is-2015' into next

f5afb90d VS: Rename VS 14 generator to 'Visual Studio 14 2015'