Use a better icon for recently accessed items in the Places Panel

The problem with the icon "package_utility_time" that has been used
before was that it is not available on all distros. The new icon
"chronometer" should be available on every KDE install.

Thanks to Elias Probst for suggesting the new icon - I'm not that
familiar with the icons provided by KDE myself.

CCBUG: 304323
(cherry picked from commit d7e7ca53)