Fix edu challenge notebook and refactor config folder

[mathpluscode]

Description

• remove config outside deepreg/
• fix edu ch related to pyyaml and recent changes
• add clarification on pypi

Fixes #386,#387

Type of change

What types of changes does your code introduce to DeepReg? Put an x in the boxes that
apply

• Bugfix (non-breaking change which fixes an issue)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Documentation Update (fix or improvement on the documentation)
• New feature (non-breaking change which adds functionality)
• Other (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR.
If you're unsure about any of them, don't hesitate to ask. We're here to help! This is
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• I have
  installed pre-commit
  and formatted all changed files.
• My commits' message styles matches
  our requested structure,
  e.g. Issue #<issue number>: detailed message.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[codecov-commenter]

Codecov Report

Merging #390 into main will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #390   +/-   ##
=======================================
  Coverage   98.65%   98.65%           
=======================================
  Files          29       29           
  Lines        1704     1704           
=======================================
  Hits         1681     1681           
  Misses         23       23           

Impacted Files	Coverage Δ
deepreg/parser.py	100.00% <ø> (ø)
deepreg/predict.py	96.42% <100.00%> (ø)
deepreg/train.py	96.00% <100.00%> (ø)

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