FEATURE : manage table columns in rdlibrary

[fpeyraud]

Hello
Some users are massively using the "year" field from the carts to organize their scheduling. They would love to have this column available in rdlibrary list so that they can order carts by year.
More generally, it could be useful to have a contextual menu in table headers in order to add and remove columns
By the way, it could be useful to store in the .rivendell/rdlibraryrc preference file the current column and ascending/descending order, and maybe the last filter and GROUP/SC selection