Move Geometry inheritance to Geometry attribute

GanttDiagram inherit from Geometry because it needs to convert trace time to render units. The different kinds of Render (Render_alternate, Render_svg...) also inherit from Geometry to convert render units to screen pixel units.

Geometry needs the current scaling along x or y axis to convert one units to another. Before Info refactoring (commit 63dc9bbf) the trace length and the minimum/maximum visible times were global, so there was no problem. Now each Geometry instance has its own scale and translate.

If a GanttDiagram and a Render are used at the same time, while building the trace for example, problems can occur because the scaling aren't the same in both class. A solution could be to use a Geometry object in the Render. If a GanttDiagram is created, the Geometry object from the Render could be given (with pointer or reference) to the GanttDiagram.