Impl. extra BarcodeIndex serialisation, use conjugate edges & edges to fasta output

barcode_index.hpp:
- Implemented taxa_codes + taxonomy_ serialisation
- Made taxa_codes::map's public

barcode_info_extractor.hpp:
- Added funcs: EdgeIsValid, GetConjugateEdge, GetSequence, GetEdgeLength

barcode_index_construction.cpp:
- Added write_contigs_to_fasta for testing purposes.
- Re-implemented taxonomy assignment to use edge & conjugate.

read_cloud_connection_conditions.cpp:
- In TaxaBreakPred.: if taxonomy of edge not found, try taxonomy of
  conjugate edge. Else taxa 0.

logger.hpp:
- Created special DEBUG_SAM for personal logging. Will change at end.