Add textoutline(on/off/default)

This commit adds a new scripting command for textbox visual control,
where you're able to force the transparent textbox's outline on or off.

desktop_version/src/Textbox.cpp

@@ -43,6 +43,9 @@ textboxclass::textboxclass(int gap)
 
     image = TEXTIMAGE_NONE;
 
+    force_outline = false;
+    outline = false;
+
     crewmate_position = TextboxCrewmatePosition();
     original = TextboxOriginalContext();
     original.text_case = 1;