plot the phase guide at the correct phase

[baggepinnen]

phase guides should be shown at pm 180 deg, not at 0.

[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
:x: 0.048
:heavy_check_mark: 0.011
:heavy_check_mark: 0.001
:heavy_check_mark: 0.001
:heavy_check_mark: 0.006
:heavy_check_mark: 0.001
:heavy_check_mark: 0.0
:warning: 0.028
:x: 0.06
:heavy_check_mark: 0.0
:warning: 0.017

[codecov[bot]]

Codecov Report

Merging #802 (fc6b789) into master (dc1d477) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #802   +/-   ##
=======================================
  Coverage   97.14%   97.14%           
=======================================
  Files           4        4           
  Lines         315      315           
=======================================
  Hits          306      306           
  Misses          9        9           

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