Refacto DrawTrace

The code from DrawTrace was templated but this had no use because the type was always equal to GantDiagram. Thus DrawTrace methods were moved to the .cpp file for better code layout.

inlining has been removed because it is only useful for small functions which was not the case.

Some method were removed because they were small and only called one are two times without the need for an entire DrawTrace object.

There might still be rework to do :

• The _filter attributes inside the trace is only used for zoom in DrawTrace but is always equal to 0. I don't know if this attributes had a real intended purpose so for now I did not touch it.
• The GantDiagram object used everywhere in DrawTrace could be an attribute created with the constructor, but there will be some problem when DrawTrace is used for entity information because not GantDiagram object is created