SearchResult - mark internal properties as pseudo-private + aggregation support

[benoitvidis]

This PR slightly modifies the SearchResult objects by

• (cosmetic) making internal properties pseudo-private to get a more readable console.log
• add the aggregations support

[codecov-io]

Codecov Report

Merging #323 into 6-dev will increase coverage by <.01%.
The diff coverage is 100%.

@@           Coverage Diff            @@
##           6-dev    #323      +/-   ##
========================================
+ Coverage   97.5%   97.5%   +<.01%     
========================================
  Files         28      28              
  Lines       1400    1404       +4     
========================================
+ Hits        1365    1369       +4     
  Misses        35      35

Impacted Files	Coverage Δ
src/controllers/searchResult/profile.js	100% <100%> (ø)	⬆️
src/controllers/searchResult/document.js	100% <100%> (ø)	⬆️
src/controllers/searchResult/base.js	100% <100%> (ø)	⬆️
src/controllers/searchResult/role.js	100% <100%> (ø)	⬆️
src/controllers/searchResult/user.js	100% <100%> (ø)	⬆️
src/controllers/searchResult/specifications.js	100% <100%> (ø)	⬆️

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