[ENH] Add mrds scripts part 2

[arnaudbore]

Quick description

Script to compute FA, AD, MD, RD for each tensor found for MRDS
...

Type of change

Check the relevant options.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Provide data, screenshots, command line to test (if relevant)

Same as #1021

Checklist

• My code follows the style guidelines of this project (run autopep8)
• I added relevant citations to scripts, modules and functions docstrings and descriptions
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I moved all functions from the script file (except the argparser and main) to scilpy modules
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

Attention: Patch coverage is 41.81818% with 32 lines in your changes missing coverage. Please review.

Project coverage is 68.91%. Comparing base (2d8520c) to head (0c21c24).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1022      +/-   ##
==========================================
- Coverage   69.00%   68.91%   -0.10%     
==========================================
  Files         427      428       +1     
  Lines       22094    22158      +64     
  Branches     3297     3306       +9     
==========================================
+ Hits        15246    15270      +24     
- Misses       5563     5602      +39     
- Partials     1285     1286       +1     

Components	Coverage Δ
Scripts	69.90% <41.81%> (-0.12%)	⬇️
Library	67.49% <ø> (-0.07%)	⬇️