Rudimentary support for multipart bas files

Now when you open file.bas.h5, it figures out whether it is multipart
or not, and does the right thing.  Works by creating subordinate
BaxH5Reader objects, and proxying to them as necessary.

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122368]
Add Zmw::predictedAccuracy() method, which taps into the ReadScore

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122369]
Remove test for defunct regionTable accessor

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122370]
Rename basH5 -> baxH5 where appropriate

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122371]
Add IPD, PulseWidth accessors

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122372]
Substantial refactoring

  - Don't load regionTable entries eagerly, this is too expensive for
    users who are scanning Zmw's without loading the actual reads
  - Make some accessors into properties
  - Add Zmw::productivity property; rename Zmw::predictedAccuracy to
    Zmw::readScore

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122373]
Add tests for new accessors

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122374]
Add fancy slicing capabilities to BasH5Reader

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122375]
Eagerly load the ReadScore and Productivity datasets.

They are small enough and it makes a big difference for QC-centric
applications.

[Tracking bug 22690]

[git-p4: depot-paths = "//depot/software/bioinformatics/lib/python/pbcore/": change = 122376]