add resultset duplicates removal

[mmaelicke]

closes #196

[codecov[bot]]

Codecov Report

Merging #221 (b6020ca) into master (5f40938) will increase coverage by 0.08%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #221      +/-   ##
==========================================
+ Coverage   59.11%   59.19%   +0.08%     
==========================================
  Files          75       75              
  Lines        3549     3549              
==========================================
+ Hits         2098     2101       +3     
+ Misses       1451     1448       -3     

Flag	Coverage Δ
e2e	59.19% <ø> (+0.08%)	:arrow_up:

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

Impacted Files	Coverage Δ
metacatalog/api/find.py	58.08% <0.00%> (+0.33%)	:arrow_up:
metacatalog/util/results.py	69.91% <0.00%> (+0.81%)	:arrow_up:

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[mmaelicke]

Now the unittest is called and the error is fixed ;)