Trough fixes

[freezy]

• Add proper support for opto switches, which have different timing and also have the close status inverted.
• Fix single ball trough
• Update documentation

TODO

• Add jam switch support, because it needs to be inverted for optos.
• Fix test coverage

@jsm174 or @ecurtz can you review the doc please?

[codecov]

Codecov Report

Merging #256 (523f5ae) into master (ba59b1f) will increase coverage by 0.03%.
The diff coverage is 86.20%.

@@            Coverage Diff             @@
##           master     #256      +/-   ##
==========================================
+ Coverage   56.76%   56.79%   +0.03%     
==========================================
  Files         159      159              
  Lines        9418     9441      +23     
  Branches      932      937       +5     
==========================================
+ Hits         5346     5362      +16     
- Misses       3848     3850       +2     
- Partials      224      229       +5     

Impacted Files	Coverage Δ
VisualPinball.Engine/VPT/Trough/Trough.cs	77.33% <84.00%> (-3.80%)	⬇️
VisualPinball.Engine/VPT/Trough/TroughData.cs	96.29% <100.00%> (+0.14%)	⬆️

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