pattern.plotter: Plot age-mixing pattern.
In wdelva/RSimpactHelp: Pre- and Post-simulation helper functions for RSimpact Cyan

Visualizes the age-mixing pattern from a Simpact-simulated population. This function takes as input a datalist produced by pattern.modeller and outputs a scatterplot of the age of the individual in the population versus the age of their partner. The plot contains a dashed line that represents a scenario where people choose partners that are the same age as themselves. Juxtaposed with this is a line that represents the population-average predicted partner ages based upon the generalised linear mixed effects model in pattern.modeller.