Qt: Show the full file path in the status bar.

Qt: Show the full file path in the status bar.

Add file_size_to_qstring and use it to show the file size. Add a
"shrinkable" property to LabelStack. Make the info status shrinkable.
Elide text so that long file paths don't widen the main window.

Change-Id: Ieb1caaf7e016384609d41fcabaa63d8f7a293eff
Bug: 10949
Reviewed-on: https://code.wireshark.org/review/7534
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>