Implement IDataView interface

[HLWeil]

Possibility of whether Frames could implement IDataView interface could be checked. This would open the door to directly injecting Frames into e.g. all sorts of machine learning algorithms implemented in ML.NET. Currently, if one wants to use both Deedle (for data preparation) and ML.NET, a transformation step is needed.

Additionally, maybe this could also be a solution for #343? Allowing for reading and writing feather/parquet would be a great addition, as they are generally faster than text based formats and also provide more type safety.

Not sure though, whether IDataView requires some amount of mutability and how this would work with Deedle Frames.