Currently we don't import existing linefilter strings to new linefilter dialog. This can be considered as dataloss if user has long and complex filter ready.
I think what we'll need to do is:
- check if there exists old filter but no new filters (as in startup of new release for a first time) then import the old filter into new
- parse the old "multiline" filter string to separate filters
- inform user about import with messagebox
- if new filters already exist, don't import old filter (to avoid importing it multiple times)
- no need to delete old filter to keep support for old release