Added Vsix projects to install MahApps.Metro project and item templates

Added Vsix projects to install MahApps.Metro project and item templates.  There are two versions.  The first version does not install any references and is for those who compile MahApps.Metro from source.  The second version uses the last stable NuGet release of MahApps (Currently 0.12.1).  The references are automatically installed via NuGet.

I am happy to maintain the solutions but I figure it is best if one of the admins creates the extension on the Visual Studio site.  If you need any help with setting this up please let me know.