[FEA] Port copying.hpp to cudf::column types

[harrism]

Is your feature request related to a problem? Please describe.

Now that #2207 is merged we need to start porting functionality to use it. This issue covers functionality defined in cudf/copying.hpp.

It may make sense to split this into multiple PRs since there is a lot of functionality covered by copying.hpp.

Describe the solution you'd like

Update the API functions definitions in cudf/binaryop.hpp and their implementations to use the new cudf::column and associated classes.

Note that until string columns and other wrapper types are supported, operations will only be able to be implemented for numerical columns. Initially the "legacy" APIs should be kept in place but moved to the cudf/legacy folder and if necessary a legacy namespace.

[harrism]

@rgsl888prabhu is there anything left from copying.hpp (other than gather/scatter) to port? If not, let's close this.

[rgsl888prabhu]

Nothing apart from scatter and gather, so we can close.