column headers are now selectable in a css sense

Also removed some code that had been commented out, such as alerts for
debugging that were no longer in use. Added additional comments for some
functions - namely the jsTree/hierarchical facet drag and drop.
added a few more comments
played with tabs
implemented array to keep track of selected cols

Also started to add callback for specifying columns for links_via, but
it doesn't quite work yet. Once it's ready, the basic functionality
should carry over to a callback for specifying for col-based
conversions, too.