Stacking now involves 3 layers: BELOW, NORMAL and ABOVE.
In each layers, floating windows are stacked above tiled windows.
The *stack* function is now extremely simple: it just inserts an item in
a sorted list, relying on *stack_cmp* to compare clients.
Fullscreen windows are no longer special.
- Expand `underlying_monitor` into `monitor_from_client` to avoid
passing a NULL pointer to `translate_client`.
- Remove the `fit_monitor` setting (use the `--center` rule effect
instead).
- Don't remap a window in it's last location (node invisibility would be
the proper way to do this).
- Call `translate_client` after configure requests.
The last desktop and monitor are now deduced from the history.
The stacking order is now independent from the history of the focused
nodes: this prevents hacks on both sides.
All windows are now considered in the stacking algorithm: it prevents
tiled windows from one monitor to appear above the floating windows of
another monitor.
Transfered windows are stacked below the windows of the same kind.
