New template: Stacked Slope Mashup (& small multiples version please too)

[fryford]

A la - https://twitter.com/mattsmithetc/status/1178977615480160261?s=20

[giacomobg]

This is kind of that but without being stacked https://onsvisual.github.io/Simple-charts/all-templates/slope-multiple/

[henryjameslau]