Add support for basic HPGL instead of HPGL/2

The current HPGL exporter creates HPGL/2 compliant files, which are often used as an interchange format with other programs. Unfortunatly HPGL/2 is not compatible with old-school plotters like the HP7475, which some (or at least me) use for manufacturing PCBs. Those old plotters only speak HPGL/1 which doesn't have a concept of PM (polygon mode) or different pen widths for example, so the original use of the file format is lost. In fact the original routine *did* output native HPGL/1 code up to commit 2284228c35bbfb070d478cd4ce01db557061b939, which is the reason why I have to use an old build of pcbnew just for exporting.

This is why I propose to re-add the old code and let the user choose which HPGL version to use. The two routines would have some code in common and only differ, where it is required (filling a wide track, generating polygons etc.).