Rework barcode API slightly, per discussion with Jim B.

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 124917]
Bump version to 0.6.4 for barcode changes

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 124927]
fixes to pbcore to work with new bas file fornat -- 2.1 bas/bax files do not have /PulseData/ConsensusBasecalls
bug 23171

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 125021]
Work with new CCS bas files which contain only the ConsensusBaseCalls
group, not the raw BaseCalls group

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 125027]