Middle-elide file/folder labels so the extension is always visible
This ensures that the filename extension is always visible, and also is just a
nicer way to elide file and folder names in general.
Icons view with limited label height:
Subscribers: GB_2, ndavis, rooty, elvisangelaccio, kfm-devel
Differential Revision: https://phabricator.kde.org/D19471