Adds basic plots

[AnderGray]

This PR adds the ability plot the following using plot recipes:

• Distributions (both pdf and cdf)
• IntervalVariables
• P-boxes
• A vector of UQInputs (plots it in a grid)
• A vector of Intervals (the ecdf of a p-box)
• A bivariate scatter of Intervals (ecdf of a bivariate p-box)

With plot recipes, various properties of the plots should be editable by the user as they would any standard plot with Plots.jl (i.e. color=:red, will make the plot red)

Eg, the following DEMO script (in demo/plotting):

using UncertaintyQuantification, Plots

X1 = RandomVariable(ProbabilityBox{Normal}(Dict(:μ => Interval(-1, 2), :σ => 1)), :X1)
X2 = RandomVariable(ProbabilityBox{Normal}(Dict(:μ => Interval(-1, 2), :σ => 2)), :X2)
X3 = IntervalVariable(-1, 2, :s)
h = RandomVariable(Normal(0.24, 0.01), :h) # height

plot(X1)    # p-box
plot(X1, color = "red") # red p-box
plot(X3)    # Interval
plot(h)     # distribution 

inputs = [X1, X2, X3, h]

plot(inputs)    # Everything together

samples = sample(inputs, 50)

plot(X1)
plot!(samples.X1)    # Interval ecdf of X1

plot(samples.X1[1], samples.X2[1])  # Plots 2D box

plot(samples.X1, samples.X2)        # Plots bivariate random sets of X1 and X2

[codecov-commenter]

Codecov Report

:x: Patch coverage is 95.06173% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/plotting/plot_recipes.jl	94.93%	8 Missing :warning:

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