Improve performance when moving groups of nodes

[ifitzpatrick]

The app is slowed down a lot when moving groups because each individual node in the group triggers an update cycle. By only calling markDirty once all of the noflo.Graph listeners have been called for each node, we can speed up this ui interaction quite a bit.

[forresto]

Smells like somewhere a refactor fluxy dataflow would help.

[ifitzpatrick]

Would we be able to avoid triggering a rerender of the whole graph view if we did that?

[jonnor]

Waiting until closeTransaction should generally be enough for this.