Simulations overlay topo info

[bacv]

Collecting and saving overlay information during the simulations runs, mainly to visualize the overlay using some other methods.

Tested on a temp branch rebased on #478, example output:

{
   "committees":[
      "0x02974c9e8c198578be860dcb020b429bd3deea540549eb0012a689c2dc6d42c8",
      "0x6e050cf62d9ed7f6a97833c6a1aeb663f8bbbe4b3ebb731e7bfba4cfd988cd94",
      "0xd567dae8d1c8163959f3577cbb44c9dc051af265a89f49009efada79623efb5f"
   ],
   "committee_sizes":{
      "0x02974c9e8c198578be860dcb020b429bd3deea540549eb0012a689c2dc6d42c8":3,
      "0xd567dae8d1c8163959f3577cbb44c9dc051af265a89f49009efada79623efb5f":3,
      "0x6e050cf62d9ed7f6a97833c6a1aeb663f8bbbe4b3ebb731e7bfba4cfd988cd94":4
   },
   "edges":[
      [
         "0x6e050cf62d9ed7f6a97833c6a1aeb663f8bbbe4b3ebb731e7bfba4cfd988cd94",
         "0x02974c9e8c198578be860dcb020b429bd3deea540549eb0012a689c2dc6d42c8"
      ],
      [
         "0x6e050cf62d9ed7f6a97833c6a1aeb663f8bbbe4b3ebb731e7bfba4cfd988cd94",
         "0xd567dae8d1c8163959f3577cbb44c9dc051af265a89f49009efada79623efb5f"
      ]
   ],
   "next_leader":"0x0000000000000003000000000000000000000000000000000000000000000000",
   "root_id":"0x6e050cf62d9ed7f6a97833c6a1aeb663f8bbbe4b3ebb731e7bfba4cfd988cd94"
}

[danielSanchezQ]

You can make it require Overlay as well to constrain it more, but it ok like that if we want to have some mock at some point:

pub trait OverlayInfoExt : Overlay

[bacv]

I'm leaning towards leaving it as is for now, until it's required. As I understand, the implementation definition (impl<T: Overlay> OverlayInfoExt for T {) wouldn't change with pub trait OverlayInfoExt : Overlay?

[danielSanchezQ]

Nice!