try at robust subplot-to-subplot selections
try at robust subplot-to-subplot selections

- clear selection outlines when mousing down on different subplot
  than last selection
- do not try to merge selection polygons from different subplots
- rm (now obsolete) splom-only clearSelect calls from cartesian/select.js

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