Replace backlinks list with a LiveData in the Page Information tab

Existing Live Data sources currently cannot display backlinks. So we first need a data source for this. I would suggest to implement a generic Solr search Live Data data source that can then be used (or specialized) for this purpose. It doesn't need to have a lot of features for a first version, just supporting title and link with an arbitrary Solr query as input could be enough for a first version. We could then add support for more fields as we need them.