editor_services was growing into one interface every tool depended on
whole. It splits into the roles the editor plays for its tools: the
selection, the view, the undo history, the templates by the track, the
ground with the terrain model, the track design and the guide of the
first steps. Each tool is handed only the roles it uses, so what it
depends on can be read from its constructor; editor_services stays as
the sum of the roles the editor implements.
The fourth tool out of editor_mode. The track under the cursor and the
first steps of the tutorial become types of their own, which the editor
gives to the tools, and a tool shown as a tab of the lineside panel keeps
its open and expanded flags in a tool_tab. The trainsets waiting for the
save are handed to the editor by the tool, which hears back when they
were written. The self-test command trainset moves with it.
