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.