Add support for setting units on the FBX writer

Some software need specific units, and it seems not to be possible to change it afterwars in the FBX ASCII file in an editor, so this is needed.

I'm stuck here as well.

This seems to show how the Autodesk FBX SDK handles units - or ? http://help.autodesk.com/view/FBX/2019/ENU/?guid=FBX_Developer_Help_nodes_and_scene_graph_fbx_scenes_scene_axis_and_unit_conversion_html

According to the logfile (FME v2020.2) the FBX writer defaults to cm units. As a workaround you can add a scaler before the writer. I found scaling by 100,100,100 (x,y,z) worked for me.