Node Library Management v02

We need to rectify the concept of node libraries and linking. Right now, they're referenced to a single dag, and the available nodes show up in each DAG. That should not be necessary. It should probably be its own floating window. Also, the libraries can probably be automatically added rather than called out by the user. But does it make sense to explicitly keep a list of referenced libararies in a dag? One could find this by checking the nodes...