store: copy root family data to cycle point nodes

[oliver-sanders]

Follow on from #1108

Currently the data store "stores" cycle point data in the root family node.

I.E:

workflow
  .children[:]
    .familyTree
      .children[0]
        .node

This is because we don't actually have a way of querying cycle points, all we can do is to query the root family for each cycle.

We should probably sync the "root" family data with the cycle point data in order to make it easier to access.

Pull requests welcome!