Overview: fix some keyboard navigation quirks
In the overview, you have to press tab or down just to start navigating since at the beginning no window is highlighted or, worst, the window that randomly falls under the mouse pointer is highlighted making the entire experience very confusing: first a random window is highlighted, then you press tab or down and the first window is highlighted...
I think the first window should start already highlighted (to spare the user one key press) and only if the mouse is moved the window below the mouse pointer should be highlighted.