Added new config option 'load-chunk-on-request' in bukkit.yml.

This will be set to true by default until I fix all chunkloading issues
with this flag off.
Note: If you are experiencing performance issues and do not need any
chunks force-loaded, try disabling this setting.

* Added loadChunkOnProvideRequest for transferPlayerToDimension to fix
issues such as Twilight Forest's teleport not loading chunks properly
before spawn.