Enable loading and using offsets from custom sprites.

Currently, the program inherits offsets in custom sprites from the old graphics. This works as long as the new psrites have equal layout. New sprites that do not follow this layout, will fail to get rendered at the right spot.

The Graphics repo PR #5 changes the sprite file format to include custom offsets. This patch enables CorsixTH to read and use those new files
- Sprite offsets are not added to the position in the animation manager, but passed on to the actual sprite renderer. I added ZERO_XOFFSET and ZERO_YOFFSET to be clear where this happens.
- Custom offsets of new sprites are stored while loading. Old graphics are supported by disabling usage of this new offset.
- The sprite draw routine is extended to replace the provided offsets from the animation manager by its own offsets for the sprite if the bUseOffsets allows it.
- The sprite file version number is incremented to match with the new file format created after applying Graphics PR #5 to the encoder

While this works for the static sprites, I have doubts it will nicely work for animations too. In hindsight, I should have modified animations instead of sprite loading, perhaps?