[ReloadStopButton] Instead of pausing updates, only update the button after delay
[Cleanup] QTimer::start() restarts timer if it is already running
[Models] Decrease the delay for filtering to 300ms
[SaveSettings] Don't save settings twice on app close
[BookmarksImport] Show full structure of imported bookmarks

BookmarksModel can now be used with arbitrary root item independently
of main bookmarks root item.