Get Columns

[graysonarts]

From conversations with @t8y8 , we need the ability to get the list of columns in a datasource.

[benlower]

are we getting fields or getting columns? or is it both? just want to make sure we're consistent on what we're calling things.

[graysonarts]

fields = columns. I think we use columns everywhere, so I standardized on that
Fixed the issue with that assumption.