Improve bqplot classic theme
Improve bqplot classic theme

bloomberg/bqplot,bloomberg/bqplot,SylvainCorlay/bqplot,ChakriCherukuri/bqplot,SylvainCorlay/bqplot,bloomberg/bqplot,ChakriCherukuri/bqplot,ChakriCherukuri/bqplot,SylvainCorlay/bqplot