* Bump MSBuild Version to 15.1.0-preview-000503-01
* tool_csc->tool_roslyn
* pull some properties up to dir.props
* Move Roslyn to "Roslyn" subdirectory
* Fix relative paths in RunCsc.*
* Add removal of csc & vbc from deps.json
* Revert roslyn to 2.0.0-rc3-61212-03
* netcoreapp -> 1.0.3