This is the first step towards a generic backbone to connect
any GUI elements to the session within Proc-Layer.
It is based on a spefic understanding of Model-View-Controller,
which turns the Model-Controller interactions into messages.
the rules are:
- our own headers go before any library headers
- all headers need to be spelled relative to include root
- ensure that gtk is always included via gui/gtk-base.hpp
DisplayService is intended to implement the Display facade and additionally
manage N display output sinks (DisplayerSlot). Now the playback-controller
contains just the bare controller logic, all services like tick generation
or signal dispatching have been factored out... makes me feel better :-)
this allows the C++ version to provide automatic lifecycle management for
the play process, while both versions of the API (C and C++) impose only
one level of indirection.
