Add "English sprites" setting

It'll start working in the next commit... See the description there.

(This commit does not add the new strings to the language files, since
Terry now added them separately in his own branch)

desktop_version/src/Localization.cpp

@@ -16,6 +16,7 @@ bool pre_title_lang_menu = false;
 
 std::string lang = "en";
 std::string lang_custom = "";
+bool english_sprites = false;
 std::string new_level_font = "";
 LangMeta langmeta;