Checkpointing work.  Refs #7336.

Expanded AlignAndFocusPowder to reduce low resolution data in addition.
Make SNSPowderReduction to support low resolution TOF.  Refs #7336.
Checkpointing work.  Refs #7336.
Checkpointing work.  Refs #7336.

1. Conjoin the low resolution TOF workspace to output workspace;
2. Enable to use offset on spectrum number of the spectra from low
resolution TOF workspace;
3. Refactor codes
Merge branch 'feature/7336_sns_reduce_lowres' into develop