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/CustomLevels.h

@@ -6,7 +6,6 @@
 #include <SDL.h>
 #include <string>
 #include <vector>
-#include <map>
 
 class CustomEntity
 {