* Add SSZ Unions through case objects
* Add connection id content response test and improve other test vectors
* Implement content keys and ids for state network as per spec
Content keys case object is used so that it can be serialized and
deserialized as an SSZ Union.
* Let message Union in Portal wire protocol start at 0 as per new spec
- Search for the node on an incoming portal message and try to add
it to the routing table
- Don't rely on discv5 nodes for bootstrapping portal networks for
now.
- Attempt to repopulate the routing table when it is at 0 or drops
to 0.
* Allow for passing Portal specific bootstrap nodes
* Fix to also replaceNode when decodeMessage fails
* Add portal bootstrap node tests and reorder test cases
Kim De Mey
KonradStaniec