applets/taskmanager: make textual list become the default option
"Cycle through grouped tasks" is not a useful behavior when there are more than 2 windows in a group. The user will usually have to click multiple times to activate a window and the order of activation is unknown. Textual list is more useful in that case, each window is listed in the grouped dialog so the user can activate a task by clicking only twice.
Edited by Fushan Wen