Window manager

This package provides the central part of Genode's componentized GUI stack
via a custom implementation of the nitpicker session interface.
It must be complemented by a window layouter and a window decorator, each of
which is a separate client component. Whereas the window decorator defines how
windows look, the window layouter defines how they behave.

The window manager, decorator, and layouter propagate their respective state
(like the window layout or the decoration margins) via reports and ROMs. The
window-manager package manages the flow of information between those parties
by providing a report and ROM service to the external layouter and decorator.

The special roles of the layouter and decorator among the window-manager
clients are identified according to their names (labels), which are suffixed
with "layouter" and "decorator" respectively. All other clients are expected
to be regular windowed applications.