The labels of clipboard ROM and clipboard report sessions of WM clients
must be consistent with the client's nitpicker label. Hence, we must
route those sessions through the window manager, analogously to the
approach taken for shape reports in #3165.
Issue #3437
This commit replaces the former floating_window_layouter with a new
window_layouter component that supports the subdivision of screen space
into columns and rows, the concept of layers, and the principle ability
to store window layout information across reboots. The latter is
accomplished by reflecting the component's internal state as a 'rules'
report to the outside.
Fixes#3031
