window ui: remove depricated use_action_appearance property
gitignore: ignore backup files *~
filter: use visible column instead of callback. this is quite a bit faster
ui: set fixed row height, which sould make it faster
clear the search text when hidding the window to speedup the next show
make_default_entry_selection: use different iteration (-> a bit faster?)
select_item_path: call scroll_to_cell on idle to minimize ugly update artifacts
filtering: add an abortable background thread to filter (much faster now)

the thread uses a semaphore to know when to filter & stores the results
in an array, then notifies the ui thread to update the list.
if in the meanwhile the filter changed, the thread gets aborted & restarts.