Implement loading of .meg files using the Resource manager

- I extract pixel data from the resource without using QuickDraw
- Both resource-fork and data-fork .meg files work

Related changes:
- The custom graphics textures are now wrapped in a custom class
- bmp images are loaded if a meg is not found

Incidental changes:
- Various TODO notes
- Fix cScenario::spec_strs skipping several strings and potentially fetching out-of-bound entries
- oopsError now uses string streams instead of sprintf

osx/boe.fileio.cpp

@@ -96,7 +96,7 @@ fs::path progDir;
 //	ave_tr_type ave_t;
 
 //template_town_type town_template;
-sf::Texture* spec_scen_g = NULL;
+cCustomGraphics spec_scen_g;
 
 std::ofstream flog("bladeslog.txt");
 void init_directories()