fixed labelAlignments to include index column

Changed pbbarcode.py labelAlignments function to include 6 columns in the destination cmpH5 file. The first column is the index of the barcode, as described in [this documentation](https://github.com/PacificBiosciences/pbbarcode/blob/master/doc/PbbarcodeFunctionalSpecification.rst#additions-to-the-compare-hdf5-cmph5-file). The resulting cmpH5 file can then be correctly split using this command:
```
cmph5tools.py select --where "Barcode != '--'" --groupBy Barcode $ALN
```