Implemented removing peaks.  Refs #7652.
Cleaned the code.  Refs #7652.
Enhancing UI and background selection.  Refs #7652.

1. Add visibilities to properties used by specific functions of the
algorithm;
2. Add more support to fit Chebyshev background function.
Added default value to boundaries.  Refs #7652.
Added an option to read in a background function.  Refs #7652.
Added unit test and cleaned code.  Refs #7652.
Fixed some properties issue.  Refs #7652.
Merge remote-tracking branch 'origin/feature/7652_process_bkgd'