Unhardcode textbox colors in textbox arguments

There's a few places where textboxes are constructed through code, but
they pass in the color's RGB values in manually. This commit
unhardcodes most of them them, replacing them with a color lookup.

The ones that weren't changed are special cases, like `175, 174, 174`.

desktop_version/src/Script.h

@@ -9,7 +9,11 @@
 
 #define filllines(lines) commands.insert(commands.end(), lines, lines + SDL_arraysize(lines))
 
+#ifdef SCRIPT_DEFINITION
+#define TEXT_COLOUR(a) textbox_colours[a]
+#else
 #define TEXT_COLOUR(a) script.textbox_colours[a]
+#endif
 
 struct Script
 {