Plot networks about bqplot

[SylvainCorlay]

cc @SSunkara

[ssunkara1]

@albop This looks great!!!

1. Moving the nodes will be easy now. We can have drag on the Scatter and keep the Lines in sync with it. I can write up a quick example for that. The easiest way to do this would be to have the drag behavior on Lines with markers so that we need not do they sync stuff manually. This is part of the bigger to do, which is to add Scatter events to Lines with markers. Once we have that it should be very straight forward.
2. Arrows, I am not sure if this will be very quick. We can add another Scatter with the Markers as arrows. This angle can be set using the skew or rotation attribute of the Scatter. Again, I will come up with a small example for this.
3. Labeling the nodes will be very easy. You can add names attribute to the Scatter.

P.S.: Sorry for the late response. :(

[dmadeka]

@albop Closed by #483

[fpom]

Moving the nodes will be easy now. We can have drag on the Scatter
and keep the Lines in sync with it. I can write up a quick example for that.
The easiest way to do this would be to have the drag behavior on Lines
with markers so that we need not do they sync stuff manually. This is part
of the bigger to do, which is to add Scatter events to Lines with markers.
Once we have that it should be very straight forward.

Sorry to come back to this old issue, but you say that allowing to drag nodes would be easy to implement. However, it seems that the bqplot.marks.Graph does not allow it when nodes are placed using x and y attributes. I'm wondering if it can be made in this case.

Arrows, I am not sure if this will be very quick. We can add another Scatter
with the Markers as arrows. This angle can be set using the skew or rotation
attribute of the Scatter. Again, I will come up with a small example for this.

On this point also, I'd be interesting to know if something has been done also. I know that directed graphs can have arrows, but they are placed in the middle. I'd be interested in adding arrow at the tips of edges (and varied sorts of arrow if possible). I thinks I could do the maths to compute the arrow tips positions and angles, but I'd do it from Python, perhaps we can let D3 do it instead.

Thanks in advance for your answer!
Franck