Advanced data column selector

[guerler]

Suggested by @bgruening: It would be nice to allow an overwrite mode like in the workflow form. So a user could choose to insert numbers instead of choosing the fields.
I get this request now a lot in communities that do more statistics on large files (>30 columns).

This PR (galaxyproject/tools-devteam#511) demonstrates a simple tool that can take 2-3 as an indicator of the columns instead of 2,3. Tests are passing, maybe you can use this to explore some UI options? The idea is to offer the user some more advances selections like 2,5,10-30,40 in an advanced mode next to the traditional data_column view.