Minor fixes to clean up pipelines.py

[GregConan]

Changes suggested to app/pipelines.py during 2022-02-02 code review:

Replace/modularize redundant code listing arguments

• Some redundant code used by many of the classes could be replaced with a common function or something because (especially the 'spec' variable) in many of the classes reuses a lot of the same arguments
  • Specifically these functions: PreFreeSurfer (lines 684-694), FreeSurfer(lines 684-694), PostFreeSurfer (lines 712-740), FMRIVolume (lines 750-774), FMRISurface (lines 838-849), and DCANBoldProcessing (lines 872-891)

Clean up specific classes

ParameterSettings class

• Line 19. Finish this unfinished sentence
• Lines 25-28. 1mm is mislabeled as 0.7mm here, so fix the labeling
• Lines 52-75. Cite that these magic numbers came from the original HCP pipeline
• Lines 76-92. Cite that these magic numbers came from DCANBoldProc defaults
• Lines 118-174. Clean up this block
• Lines 179-184. "These are straight-up lies," per Audrey H, and "false promises," so they should be deleted
• Lines 197-199. Delete this block that was commented-out around 2018

PreFreeSurfer class

• Line 665. "else" is not aligned with the "if" it refers to on line 662

DiffusionPreprocessing class

• Lines 954-971. Remove all of these lines because they were never implemented.
  • That was planned 3 years ago and never implemented