data type + reference genome filter on homepage does not work with virtual studies

[tmazor]

If I apply the data type filter, it does not work with virtual studies -- eg if I create a virtual study from a study with mutation data, then apply the filter on the homepage for studies with mutations, my virtual study disappears even though it has mutation data

[TJMKuijpers]

In addition: the reference genome filter also ignores the virtual studies.