move anything defined in FSharp.Data namespace to a better location

[smoothdeveloper]

This is taking the spirit of what is written there regarding FSharp.* namespaces: https://github.com/fsharp/fsharp.github.io/blob/master/_posts/2014-09-19-fsharp-libraries.md

We need to avoid pollution of the FSharp.* namespace, particularly by unfinished projects.

and considering that this repository is stepping over https://github.com/fsharp/FSharp.Data by having several types directly defined under FSharp.Data.

It will be a breaking changes for consumers using public types/members there, but easily fixed by opening the TBD correct namespace.