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
Modified SNSPowderReduction for low resolution.  Refs #7336.
Intended to catch a segmentation fault.  Refs #7336.
Added check on some input vectors size.  Refs #7336.
Fixed an error.  Refs #7336.
Checkpointing work.  Refs #7336.
Fixed the system test and a memory leak.  Refs #7336.
Add an information output.  Refs #7336.
Cleaned the code.  Refs #7336.
Fixed the reported issue.  Refs #7336.
Merge remote branch 'origin/feature/7336_sns_reduce_lowres'