gstlal-inspiral: merge Data and Handler

- move Handler to its own module
- rename .gen_psd_xmldoc() to .__get_psd_xmldoc() following conventions used in inspiral.Data
- inspiral.py: excise gracedb code from Data object, encapsulate in GracedBWrapper class
- remove now unused write_psd_fileobj() from reference_psd.py
- move Data class to lloidhandler.py
- rename ._gatehandler() .__gatehandler() for consistency
- remove .flush(), unused locking wrapper of .__flush()
- remove .do_gracedb_alerts(), unused locking wrapper of .__do_gracedb_alerts()
- excise eye candy from Data class, move to stand-alone EyeCandy class
- merge what remains of Data and Handler into a single class
- excise segment tracking from result, move to stand-alone SegmentsTracker class
- use Handler's PSDs for GracedB uploads instead of getting new ones
  (addresses a FIXME)