Add UC plot recipe

[guilhermebodin]

It looks like this just by doing plot(model, ks). Closes #232

[codecov]

Codecov Report

Merging #237 (3930ba7) into master (7a24d1e) will decrease coverage by 0.20%.
The diff coverage is 85.41%.

@@            Coverage Diff             @@
##           master     #237      +/-   ##
==========================================
- Coverage   93.74%   93.53%   -0.21%     
==========================================
  Files          24       25       +1     
  Lines        1886     1934      +48     
==========================================
+ Hits         1768     1809      +41     
- Misses        118      125       +7     

Impacted Files	Coverage Δ
src/StateSpaceModels.jl	100.00% <ø> (ø)
src/models/unobserved_components.jl	87.33% <81.25%> (-0.46%)	⬇️
src/visualization/unobserved_components.jl	87.50% <87.50%> (ø)

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[raphaelsaavedra]

I wonder if we should think about having a separate StateSpacePlots package in order to avoid depending on Plots to improve compilation time of the package

[guilhermebodin]

It does not depend on plots, it depends on RecipesBase, which is very light.

name = "RecipesBase"
uuid = "3cdcf5f2-1ef4-517c-9805-6587b60abb01"
author = ["Tom Breloff (@tbreloff)"]
version = "1.1.1"

[compat]
julia = "1"

[extras]
Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

[targets]
test = ["Test", "Random"]