Extended support of MMU segmentation backed for more than three colors.

Serialization and deserialization in TriangleSelector were extended to support up to 16 materials (3 unused states left for possible later extension). These changes also affect the encoding of data from custom supports and seams, but it is backward compatible with the previous encoding. And for custom supports and seams, it is produced exactly the same data encoding as before.

src/libslic3r/PrintObject.cpp

@@ -1918,7 +1918,8 @@ void PrintObject::_slice(const std::vector<coordf_t> &layer_height_profile)
     size_t region_count_before_change = this->num_regions();
     std::vector<std::vector<std::pair<ExPolygon, size_t>>> segmented_regions = multi_material_segmentation_by_painting(*this);
     // Skip region with default extruder
-    for (size_t region_idx = 1; region_idx < 3; ++region_idx) {
+    const size_t num_extruders = this->print()->config().nozzle_diameter.size();
+    for (size_t region_idx = 1; region_idx < num_extruders; ++region_idx) {
         std::vector<ExPolygons> c_layers(m_layers.size());
         for (size_t layer_idx = 0; layer_idx < m_layers.size(); ++layer_idx) {
             for(const std::pair<ExPolygon, size_t> &colored_polygon : segmented_regions[layer_idx]) {