ENH: add custom gcode back

Add custom gcode back, which can be inserted in
gcode viewer layer slider.

Signed-off-by: salt.wei <salt.wei@bambulab.com>
Change-Id: I270cc438bedf11b30f07f8f9bad6ae5436d5a2dd

src/libslic3r/PrintConfig.cpp

@@ -1565,6 +1565,15 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvanced;
     def->set_default_value(new ConfigOptionString(""));
 
+    def = this->add("template_custom_gcode", coString);
+    def->label = L("Custom G-code");
+    def->tooltip = L("This G-code will be used as a custom code");
+    def->multiline = true;
+    def->full_width = true;
+    def->height = 12;
+    def->mode = comAdvanced;
+    def->set_default_value(new ConfigOptionString(""));
+
     {
         struct AxisDefault {
             std::string         name;