Add "kpm wrap" command

- Add CsprojDumper, a tool used to dump csproj references
- "kpm wrap" creates project.json wrappers for csprojs in 'wrap' folder
- "kpm wrap" updates global.json to include 'wrap' folder as sources

parent #827 
This logic should use the nuget config API to resolve the repository path, then create the path where individual packages exist. NuGetPackage should have a Path property which represents where it is installed on disk. From there you just need to see if the assembly directory is under any of those folders.