NEW: Official filament color selection approved

- Add a filament picker dialog for official color selection
- Enable displaying multiple filament colors in the picker dialog and preview sidebar
- Introduce two new config options:
  - `filament_multi_colors`
  - `filament_color_types`
  to both the application config and the 3MF config

jira: STUDIO-12346

Change-Id: I66f8c1ec9147df4f5948c8a329c1737551280e63
(cherry picked from commit 522dc0bbca49033a1ba9725ca7f6c3ea729691a6)

src/libslic3r/PrintConfig.cpp

@@ -57,7 +57,7 @@ namespace Slic3r {
 
 const std::vector<std::string> filament_extruder_override_keys = {
     // floats
-    "filament_retraction_length", 
+    "filament_retraction_length",
     "filament_z_hop",
     "filament_z_hop_types",
     "filament_retract_lift_above",
@@ -2164,6 +2164,14 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionStrings { "" });
 
+
+    def = this->add("filament_multi_colour", coStrings);
+    def->set_default_value(new ConfigOptionStrings{""});
+
+    // 0: gradient color, 1: default color(single or multi color)
+    def = this->add("filament_colour_type", coStrings);
+    def->set_default_value(new ConfigOptionStrings{"1"}); // Init as default color
+
     //bbs
     def          = this->add("required_nozzle_HRC", coInts);
     def->label   = L("Required nozzle HRC");