add changelog for v1.56.0  - also add thank you message for some 2020 sponsored features
add changelog for v1.56.0
 - also add thank you message for some 2020 sponsored features

plotly/plotly.js,etpinard/plotly.js,aburato/plotly.js,etpinard/plotly.js,etpinard/plotly.js,plotly/plotly.js,plotly/plotly.js,plotly/plotly.js,aburato/plotly.js