Move the LuaLibrary definition into its own file

modules/onscreengui/include/gui.h

@@ -61,7 +61,7 @@ public:
 
     void render();
 
-    static openspace::scripting::ScriptEngine::LuaLibrary luaLibrary();
+    static openspace::scripting::LuaLibrary luaLibrary();
 
 //protected:
     GuiHelpComponent _help;

modules/onscreengui/src/gui.cpp

@@ -499,7 +499,7 @@ void GUI::render() {
     ImGui::End();
 }
     
-scripting::ScriptEngine::LuaLibrary GUI::luaLibrary() {
+scripting::LuaLibrary GUI::luaLibrary() {
     return {
         "gui",
         {