[ENH] GEO data sets: fix categorization of variables

[lenatr99]

Description of changes

Modified init.py file to correctly categorize the GEO Data Sets variables as discrete variables not as string variables.

Includes

• Code changes
• Tests
• Documentation

[codecov-commenter]

Codecov Report

Merging #342 (b59270c) into master (7231292) will decrease coverage by 0.60%.
Report is 56 commits behind head on master.
The diff coverage is 50.80%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #342      +/-   ##
==========================================
- Coverage   48.96%   48.36%   -0.60%     
==========================================
  Files          63       67       +4     
  Lines       10800    10907     +107     
==========================================
- Hits         5288     5275      -13     
- Misses       5512     5632     +120     

Files Changed	Coverage Δ
orangecontrib/bioinformatics/ncbi/gene/config.py	100.00% <ø> (ø)
...ontrib/bioinformatics/widgets/OWClusterAnalysis.py	0.00% <0.00%> (ø)
...ontrib/bioinformatics/widgets/OWDatabasesUpdate.py	0.00% <0.00%> (ø)
...rangecontrib/bioinformatics/widgets/OWGOBrowser.py	0.00% <0.00%> (ø)
...trib/bioinformatics/widgets/OWGeneSetEnrichment.py	0.00% <0.00%> (ø)
...rib/bioinformatics/widgets/OWKEGGPathwayBrowser.py	0.00% <0.00%> (ø)
...ib/bioinformatics/widgets/OWSingleSampleScoring.py	0.00% <0.00%> (ø)
...ngecontrib/bioinformatics/widgets/OWVolcanoPlot.py	0.00% <0.00%> (ø)
...gecontrib/bioinformatics/widgets/OWdictyExpress.py	0.00% <0.00%> (ø)
...trib/bioinformatics/widgets/utils/gui/gene_sets.py	17.69% <0.00%> (ø)
... and 19 more

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