All build dependencies available and undrag bug fixed

I've made some changes and now it is easy to configure and build raphael packages, just run "npm install". 
Also, there was a bug with undrag method. If during dragging you needed to delete an actual svg node, raphael would start raising errors, because function dragMove was still trying to reach deleted element. It was happening due to the fact, that 'drag' array which contained current elements for dragging needed to be cleaned on undrag call.