Refactor Nonlinear dimensionality specification

[ThijsvdLaar]

• Refactor dimensionality specification as Tuple
• Refactor nonlinear update specifications
• Remove need for manually specifying variate types for Nonlinear{Sampling}
• Additional rules for Nonlinear{Sampling}

[codecov-commenter]

Codecov Report

Merging #187 (1629798) into master (b10b720) will increase coverage by 0.39%.
The diff coverage is 88.34%.

@@            Coverage Diff             @@
##           master     #187      +/-   ##
==========================================
+ Coverage   86.21%   86.60%   +0.39%     
==========================================
  Files          95       95              
  Lines        4462     4406      -56     
==========================================
- Hits         3847     3816      -31     
+ Misses        615      590      -25     

Impacted Files	Coverage Δ
src/engines/julia/update_rules/multiplication.jl	100.00% <ø> (ø)
src/factor_nodes/wishart.jl	94.23% <ø> (+1.63%)	⬆️
...c/engines/julia/update_rules/nonlinear_sampling.jl	63.04% <57.57%> (+4.44%)	⬆️
src/factor_nodes/sample_list.jl	76.21% <68.75%> (+2.65%)	⬆️
src/factor_nodes/gaussian_mean_variance.jl	88.67% <71.42%> (-0.21%)	⬇️
src/probability_distribution.jl	78.66% <78.57%> (-1.94%)	⬇️
src/engines/julia/generators.jl	97.67% <100.00%> (ø)
...ines/julia/update_rules/gaussian_mean_precision.jl	100.00% <100.00%> (ø)
src/engines/julia/update_rules/gaussian_mixture.jl	100.00% <100.00%> (ø)
...c/engines/julia/update_rules/nonlinear_extended.jl	100.00% <100.00%> (ø)
... and 23 more

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[albertpod]

This looks good to me! Can be merged.