Fix compile error in LayerFromImage

- LOGS is not static anymore, as there was no reason to.
- Removed redundant argument in startEngine.
- Made some public variables private, added a getter (but not a setter).
- Removed spaces before [INFO] messages, looked weird.
- Changed some comments in PluginConfig
- When BukkitWorld is null in the MapWriter, don't try to get its name,
use native world instead.