Multiple art files for object

[flamewing]

Some objects need the ability to load multiple art files, or have a range of blank tiles added before or after the art, similar to what is done for palettes. A couple examples of objects that require this feature:

• Spiker badnik from Hill Top Zone in Sonic 2: it reuses the Sol badnik's art for its body, which needs to come before the art for the Driller badnik's art
• The Sol badnik from Hill Top Zone in Sonic 2: it uses the global fireball art, which must be before the Sol badnik's art

There are more, but these should suffice to test.