Add support for exclude parameter

[zdenekjurka]

Motivation

Add support for new exclude query string parameter, that allows user to specify codenames of elements that should be excluded from API response.

Checklist

• Code follows coding conventions held in this repo
• Automated tests have been added
• Tests are passing
• Docs have been updated (if applicable)
• Temporary settings (e.g. variables used during development and testing) have been reverted to defaults

How to test

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.60%. Comparing base (e2045fe) to head (4553b37).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #391      +/-   ##
==========================================
- Coverage   93.26%   88.60%   -4.66%     
==========================================
  Files         129      130       +1     
  Lines        2775     2783       +8     
  Branches      349      346       -3     
==========================================
- Hits         2588     2466     -122     
- Misses        179      185       +6     
- Partials        8      132     +124     

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