* allow data-attachment on ProtoChunks
- moved interfaceInjection from WorldChunk to Chunk
- dataAttachment saving on ProtoChunks in ChunkSerializer
- copy attachment from ProtoChunk to WorldChunk on creation.
- make WrapperProtoChunk wrap attachment calls to WorldChunk
* add test for data-attachment on ProtoChunks, and extend testmod.
* code style and license headers
* fix typos in javadoc
* extend testmod to test setting attachment during worldgen.
* code formatting
* fix testmod: don't crash when feature isn't placed (i.e. on GameTest server)
* add warning when adding persistent attachment to chunk with status EMPTY.
* update javadoc
* update javadoc to reference ServerLivingEntityEvents#MOB_CONVERSION
Backport persistent state code
