Adding 'Open File' and 'Open File Location' to PipelineTool tree context menu.

Adding 'Open File' and 'Open File Location' to PipelineTool tree context menu.

Added IProjectItem.OriginalPath.
- For PipelineProject this replaces FullPath
- For ContentItem this replaces SourceFile
- For FolderItem this is identical to Location

Added IController.GetFullPath(string) which returns the an absolute path given a project relative path (or returns unchanged path if already rooted).