Plasmashell freezes when trying to get free space info from mounted remote filesystem after losing connection to it
Earlier plasmashell assumed that you'll get free space info immediately (which is not true in case of losing connection to server containing a mounted filesystem - statfs will wait for response forever and freeze everything since it's happening in main thread)
I moved obtaining that info into different thread so that case won't freeze anything anymore.
It creates exactly one thread per one path. If a path is already being processed, new thread won't be created.
Also I implemented a timer used to notify about broken connection after 15 seconds.
Reviewers: broulik, ngraham, davidedmundson
Reviewed By: broulik
Subscribers: ngraham, anthonyfieroni, davidedmundson, plasma-devel
Differential Revision: https://phabricator.kde.org/D14895
Backported to 5.12 LTS (sans notification due to new strings) for impact to corporate setups
(cherry picked from commit e1c19ce4daf92a14dee44b44d199672034a346c0)