Added node shapes; initial code for implementation of bitmap caching optimization
Added node shapes; initial code for implementation of bitmap caching optimization

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