Refactor is started.  Refs #6863.
Check pointing work.  Refs #6863.
Check pointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.

Made ThermalNeutronBk2BkExpConvPVoigt inherit from
IPowderDiffPeakFunction.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.
Checkpointing work.  Refs #6863.

1. Moved some status flags to interface class IPowderDiffPeakFunction.
2. Fixed some error
Enable LeBailFunction to pass unit test.  Refs #6863.
Checkpointing work.  Refs #6863.