so that the ordering code at G-code export may work directly with
pointers to PrintInstances instead of with pair of <PrintObject, copy idx>.
Also the PrintInstance knows its source ModelInstance, which allows
sorting of PrintInstances for sequential printing in the order
they appear in Plater's object list.
psWipeTower now equals to new psToolOrdering indicating that
the ToolOrdering has been calculated (only if non-sequential mode is active).
psBrim now equals to new psExtrusionPaths
psExtrusionPaths shall be the last step before psWipeTower, indicating
that all the printing extrusions are calculated for the G-code preview
slider to edit the custom per print_z color changes, tool changes etc.
Skirt loops not being honored, only producing single loop #2193
First layer skirt only has half the loops when using multiple extruders #469
The skirt generator used to prime all printing extruders at the 1st layer
if enough skirt lines were configured, while at the other layers the skirt
used to be printed with the 1st extruder printing the layer.
There was a bug introduced quite a long time ago, where not enough skirt
lines were extruded if some extruders were not needed to print the 1st layer.
Newly the skirt generator works the same way on all layers:
All the extruders planned to print a layer are primed over the skirt
if enough skirt lines are configured.
Refactoring of GCode export of color changes, extruder switches etc,
so that the "color change" like extruder switches are applied first
at the Wipe Tower / G-code export, so that adding / removing
an extruder switch at the G-code preview slider does not invalidate
slicing.
1) Don't allocate ExtruderOverrides if not necessary
2) Use boost::container::small_vector<int32, 3) for ExtruderOverrides
(usually less than 4 instances are printed))
If the Elephant foot compensation is applied to the 1st object's layer,
the uncompensated 1st object's slice is newly used for calculation
of bridges, overhans, skirt, brim, raft and supports.
Layer::slices were renamed to Layer::lslices to simplify reading
of the code, to differentiate from LayerRegion::slices.
Fixed layouts after the second opening of the dialog.
(Removing any extruder from the sequence does not cause an incorrect layout)
Validation of entered values added
(0 is not a valid value)
