ENH: Display and modification of printer presets

Change-Id: I6a38704864fd4994a845686a299bec67f1b9b9b3
(cherry picked from commit 5b0d5259571d2b1c629ba7d88101134ec4548708)

src/slic3r/GUI/OptionsGroup.hpp

@@ -24,6 +24,8 @@
 
 namespace Slic3r { namespace GUI {
 
+extern int get_extruder_idx(const DynamicPrintConfig& config, const std::string &opt_key, int cur_extruder_id);
+
 // Thrown if the building of a parameter page is canceled.
 class UIBuildCanceled : public std::exception {};
 class OG_CustomCtrl;