plot_likelihood_scape: Speciation scape
In rscherrer/epianalysis:

This is a function to visualize the speciation probability landscape in a heatmap across parameter space.

1 2	plot_likelihood_scape(data, paramspace, dim, threshold, n = 1, color_gradient)

`data`	A data frame containing trajectories in speciation cube for all simulations (in rows).
`paramspace`	The names of the two parameters to plot against.
`dim`	The variable to use as a criterion for complete speciation.
`threshold`	The threshold above which the value of the criterion variable means complete speciation
`n`	How many of the last time points to average?
`color_gradient`	Optional pair of colors for the two extremes of the gradient.