style changes for customcsv

spaces -> tabs
add text column
function to var
add some todo comments
use filterspec instead of csvtype

So we cache it in trademapper.js and pass it around
Custom CSV import works!

still needs extending to finish the job, but have now done a custom
import and it worked OK.  Some class names didn't line up between
template and code, and a data-header element was expected but hadn't
been added.

Also did some refactoring of how this was handled in the csv module.

Also standardise the HTML class names - some were "js-customcsv__xx" and
some were "customcsv__xx" - they are all now the latter.