This moves previous aspnet5 functionality to aspnetcore, aspnet5 now
derives from the aspnetcore generator and logs a warning that it's
deprecated.
This will help resolve any confusion because ASP.NET 5 is terminology
referring to the project of around a year ago. ASP.NET Core 1.0 is the
new name for the technology, and further enhancements should target .NET
Core 1.0 rather than any old vNext or preview stuff.