The menu is needed by the app switcher as well as the overview, so
make it slightly more generic and move the code to appIcon. Also add
support for drawing the menu either to the right of or below the icon.
https://bugzilla.gnome.org/show_bug.cgi?id=590563
When we have multiple windows for an application, implement the following
behavior:
* On click + immediate release, go to the most recently used
* On click, hold for 0.6s, pop up a menu with windows, filtering
the window list to just those windows.
Mouse over on the window list highlights the moused-over window.
Implement this by splitting well item into InactiveWellItem
and RunningWellItem, sharing a base class BaseWellItem.
