Add Zmw::predictedAccuracy() method, which taps into the ReadScore

[Tracking bug 22690]
Remove test for defunct regionTable accessor

[Tracking bug 22690]
Rename basH5 -> baxH5 where appropriate

[Tracking bug 22690]
Add IPD, PulseWidth accessors

[Tracking bug 22690]
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]