client/model/graph: don't send existing nodes in commit diffs
client/model/graph: don't send existing nodes in commit diffs

tlevine/rhizi,cben/rhizi,Rhizi/rhizi,cben/rhizi,shlomif/rhizi,yuvadm/rhizi,tlevine/rhizi,ozFri/rhizi,tlevine/rhizi,cben/rhizi,Rhizi/rhizi,Rhizi/rhizi,shlomif/rhizi,cben/rhizi,shlomif/rhizi,yuvadm/rhizi,ozFri/rhizi,tlevine/rhizi,ozFri/rhizi,yuvadm/rhizi,yuvadm/rhizi,ozFri/rhizi,shlomif/rhizi,Rhizi/rhizi