revamp the mode bar's createIcon to better handle custom icons
revamp the mode bar's createIcon to better handle custom icons

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