widgets/desktops: update method of fetching desktop and window properties

Based on ewmhstatus, which basically also tells XCB to not trigger more property
change events for windows if the first request failed (e.g. if the window title
couldn't be retrieved).

https://github.com/baskerville/ewmhstatus
Merge branch 'develop' of github.com:Lokaltog/wkline into develop