Various fixes to Columns interface
Various fixes to Columns interface

vascotenner/holoviews,mjabri/holoviews,mjabri/holoviews,mjabri/holoviews,basnijholt/holoviews,basnijholt/holoviews,vascotenner/holoviews,basnijholt/holoviews,vascotenner/holoviews,ioam/holoviews,ioam/holoviews,ioam/holoviews