revise drawing so it's a bit more efficient; also revise draw order of labels; fix #417
revise drawing so it's a bit more efficient; also revise draw order of labels; fix #417

rlugojr/cytoscape.js,soomin-maeng/cytoscape.js,KonstantinShemyak/cytoscape.js,rlugojr/cytoscape.js,soomin-maeng/cytoscape.js,KonstantinShemyak/cytoscape.js