Enable specifying a mapping between data view column names and TensorFlow inputs

[yaeldekel]

Currently the column names have to match the input names that are stored in the TensorFlow model. We should enable users to provide a mapping from the data view columns to the TensorFlow inputs.
We should also enable users to specify a new name for the output column.

[codemzs]

this is being done as part of TF.NET integration.