deactivate broken features from bodeplot

[baggepinnen]

This PR deactivates a lot of the "smart features" in the bodeplot since they are broken in too many cases.

• Problems with getPhaseTicks and getLogTicks #435
• Multiple systems in same plot has inconsistent display #640
• nyquistplot strange behaviour #603

The biggest problem is that if bodeplot is invoked twice, the second invocation overrides everything that was set during the first invocation. This causes x/y-ticks to be garbage and overrides user set titles and labels. Also, the automatic label G_1(s) does not increase the subscript number unless bodeplot is invoked once only, causing multiple systems to get the same label.

I have tried for a while to fix the problems, but it requires making use of a lot of internals and I didn't manage to get a robust solution. If anyone wants to commit to implementing and maintaining a really solid and robust solution that works for all backends, I'd be up for that, otherwise I say we ditch all the broken code.

[JuliaControlBot]

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Plots were compared to references. 7/11 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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✔️ 0.001
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✔️ 0.0
❌ 0.043
❌ 0.046
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[codecov]

Codecov Report

Merging #667 (31331c0) into master (becef5c) will increase coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #667      +/-   ##
==========================================
+ Coverage   86.75%   86.92%   +0.17%     
==========================================
  Files          31       31              
  Lines        3360     3305      -55     
==========================================
- Hits         2915     2873      -42     
+ Misses        445      432      -13     

Impacted Files	Coverage Δ
src/plotting.jl	86.79% <ø> (+1.19%)	⬆️

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[albheim]

I can't say I really like some of the defaults after this change, e.g. y1 and y2 labels in mag resp phase for a single curve, but then there were some problematic default before also. And it is not really that much of a problem to send in some keywords from the user side if one wants something more specific in the label.

I think it seems like a reasonable step to take. If anyone wants to specify a lot of stuff it is probably less chance we have overridden something to make that problematic, and for just quick plots we have all basic information that is needed in a format that is good enough.

[baggepinnen]

Yeah, the y1 default label Plots uses feels rather arbitrary, but then again, it's the same for every kind of plot using Plots :/
I do however prefer y1, y2 to G1, G1 :P