Cola view constructor now takes a label argument, which is a constant string or a function taking a node's data value and returning a string
Cola view now has a "label state" that can be toggled on and off. It is off by default.
When the label state is off, Cola behaves as before, showing nodes as colored circles
When the label state is on, Cola displays a placard containing the node's label. Nodes with no label (i.e., whose label function returns a falsy value - including the empty string) will not have a placard shown (they will remain circles)
User interaction (e.g. selection state, node position, etc.) remains constant across label state changes
Selection state is indicated a little differently for label nodes - focused nodes have a pink placard background, while unfocused nodes have gray; presence in the selection is indicated by a blue border, while those not in the selection have a border reflecting the node colormap
labelargument, which is a constant string or a function taking a node's data value and returning a stringCloses #81
attn: @curtislisle