PDBContainer docs update

[BvB93]

See nlesc-nano/data-CAT#38.

• Use the automodule directive for documenting the dataCAT.PDBContainer class.
• Minor cleaning of the CAT.workflows.workflow module.

[codecov]

Codecov Report

Merging #142 into master will decrease coverage by 0.00%.
The diff coverage is 76.92%.

@@            Coverage Diff             @@
##           master     #142      +/-   ##
==========================================
- Coverage   65.15%   65.14%   -0.01%     
==========================================
  Files          45       45              
  Lines        3527     3529       +2     
  Branches      596      596              
==========================================
+ Hits         2298     2299       +1     
- Misses       1084     1085       +1     
  Partials      145      145              

Impacted Files	Coverage Δ
CAT/workflows/workflow.py	75.60% <76.92%> (-0.21%)	⬇️

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