Fureniku's Roads

Just a small patch with a couple of fixes and some performance improvements :)

- Fixed some reflectors not self-adjusting correctly
- Fixed curbs trying to place themselves above decorations on the roadside (please let me know if there's any negative effects of this)
- The road factory now only requires 100 tar per recipe, down from 1000. This should make roads much cheaper to make, as people naturally will make quite a few blocks.
- The road factory logic for consuming blocks has changed, which fixes a bug that was giving people roads for just the cost of tar.
- Added a config option to disable custom rendering of machines, which might help performance on low-end machines.
- Improved face culling for roads, which should increase performance a little (and look a lot better when using shaders). As part of this change, full size blocks are now no longer considered "full" by the game engine, which should also stop that very slight shadow that was appearing on longer slopes.