ENH:move get_extruders_colors api to plater class

jira: none
Change-Id: I8c2b31d4963b01cb193b7f2a2a3650cf7252ebc5
(cherry picked from commit 3eeabc0722027b789c59130762bd57c2745cf188)

src/slic3r/GUI/Plater.hpp

@@ -492,6 +492,7 @@ public:
 
     void on_filaments_change(size_t extruders_count);
     void on_filaments_delete(size_t extruders_count, size_t filament_id, int replace_filament_id = -1);
+    std::vector<Slic3r::ColorRGBA> get_extruders_colors();
     // BBS
     void on_bed_type_change(BedType bed_type);