Add “website” type to filter the numismatic literature

I noticed that, although the numismatic literature section https://en.numista.com/literature/index.php has reference catalogues available in online format (marked as “Website”), they are hidden, and can only be found by selecting the “All types” option.

For example, the NumisMaster website can only be found by selecting the “All types” option: https://en.numista.com/literature/index.php?r=numismaster&t=&a=&c=

I think the number of reference catalogues available only in online format is high enough at this moment to add a “Website” option.

The purpose of the Literature section is not to be a directory of websites. We want to reference mainly printed material.
We still add some websites, to be used as cross-references in our numismatic catalogue. But we don't want to promote websites in the literature section in general.