Added a design document to convert the DataDescriptor class as first-classs citizen
Modifications for proposal based on discussions
Broke the lines to fit in 80 columns.
Merge pull request #206 from FrancescAlted/datadescriptor-first-class-citizen2

A design document to convert the DataDescriptor class as first-class citizen
Fix up the server sample catalog datashapes
Remove unused config obj
Adding fix from dhirschfeld comment.
Adding basic idea of the expression graph
Adding some expression nodes