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 
Reply to @davidfowl 's previous comments:
To get the entire closure, we are adding items into `projectFiles` while iterating it. So `foreach` doesn't apply here.