Open Dataset - Select Variable Dialogue should get a filter field

[barsten]

Cate GUI -> Open Dataset -> Select Varialbes dialogue

Issue: some datasets have a (very) long list of variables (first image). This is list is not ordered alphabetically. In long lists it is very difficult to find a certain variable, in particular if one does not need exactly how it is called (AOT or AOD, for example). A filter field like it exists when looking for a datasets within a data store would be very helpful (second image).