Stacklet 1.1.1

Fixes an empty gap in the layout when one of the windows was on another Activity. Stacklet now only tiles windows on the current Activity, and re-tiles when you move a window to another Activity or switch Activities. A dragged width is kept when you visit an empty Activity.

New tests: tests/activities/run.sh (runs Plasma's activity service in a private virtual KWin) and tests/dialogs/run.sh (dialogs, About boxes and tool windows stay floating).