Network protocol upgrades (#2345)

This provides a number of upgrades to gossipsub and discovery. 

The updates are extensive and this needs thorough testing.

beacon_node/network/Cargo.toml

@@ -15,7 +15,6 @@ slog-term = "2.6.0"
 slog-async = "2.5.0"
 logging = { path = "../../common/logging" }
 environment = { path = "../../lighthouse/environment" }
-discv5 = { version = "0.1.0-beta.3" }
 
 [dependencies]
 beacon_chain =  { path = "../beacon_chain" }