Fix Yakuake icon appearing in taskbar through Qt::Tool window flag
So far we've been setting _NET_WM_STATE_SKIP_TASKBAR ourselves, but Qt messes with this, leading to race conditions where it still appears in the taskbar. This sets the Qt::Tool window flag, which will set it via Qt itself, and won't be clobbered. An old hack has been removed, as it isn't needed anymore.
Also makes show animation match retract animation.