Add dataset reference to dataset decorator

[scottgigante-immunai]

This PR adds a link to the original reference to the dataset decorator. There are some outstanding datasets I couldn't find a reference for.

[codecov]

Codecov Report

Merging #500 (849f77f) into main (5932f0a) will increase coverage by 0.03%.
The diff coverage is 97.43%.

@@            Coverage Diff             @@
##             main     #500      +/-   ##
==========================================
+ Coverage   93.68%   93.71%   +0.03%     
==========================================
  Files         103      102       -1     
  Lines        2595     2595              
  Branches      131      131              
==========================================
+ Hits         2431     2432       +1     
  Misses        114      114              
+ Partials       50       49       -1     

Flag	Coverage Δ
unittests	93.71% <97.43%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...oblems/data/Wagner_2018_zebrafish_embryo_CRISPR.py	0.00% <0.00%> (ø)
...gration/batch_integration_graph/datasets/immune.py	100.00% <ø> (ø)
...ation/batch_integration_graph/datasets/pancreas.py	100.00% <ø> (ø)
...ty_reduction/datasets/human_blood_nestorowa2016.py	100.00% <ø> (ø)
..._reduction/datasets/mouse_blood_olssen_labelled.py	100.00% <ø> (ø)
...problems/tasks/label_projection/datasets/cengen.py	100.00% <ø> (ø)
...oblems/tasks/label_projection/datasets/pancreas.py	100.00% <ø> (ø)
...ks/label_projection/datasets/tabula_muris_senis.py	100.00% <ø> (ø)
...blems/tasks/label_projection/datasets/zebrafish.py	100.00% <ø> (ø)
...ks/multimodal_data_integration/datasets/citeseq.py	100.00% <ø> (ø)
... and 20 more

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[LuckyMD]

looks good to me! URLs all seem to be correct!

[scottgigante-immunai]

Thanks!