apply numerical balancing before plotting

[baggepinnen]

Frequency-response calculations can suffer from poor accuracy for very poorly balanced models. In plotting functions, we can perform defensive balancing automatically since these are seldom performance critical. We still require to user to handle balancing elsewhere though since it changes the state representation and requires some allocations etc.

mitigates #835

[codecov[bot]]

Codecov Report

Merging #836 (441a7a1) into master (a5db7d9) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #836   +/-   ##
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  Coverage   97.14%   97.14%           
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  Files           4        4           
  Lines         315      315           
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  Hits          306      306           
  Misses          9        9           

[JuliaControlBot]

This is an automated message. Plots were compared to references. 11/11 images have changed, see differences below. After pulling this PR, please update the reference images by creating a PR to ControlExamplePlots.jl here. Difference	Reference Image	New Image
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:x: 0.06
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