Upgrade to tokio 0.3 (#1839)

## Description

This PR updates Lighthouse to tokio 0.3. It includes a number of dependency updates and some structural changes as to how we create and spawn tasks.

This also brings with it a number of various improvements:

- Discv5 update
- Libp2p update
- Fix for recompilation issues
- Improved UPnP port mapping handling
- Futures dependency update
- Log downgrade to traces for rejecting peers when we've reached our max



Co-authored-by: blacktemplar <blacktemplar@a1.net>

testing/eth1_test_rig/Cargo.toml

@@ -5,9 +5,9 @@ authors = ["Paul Hauner <paul@paulhauner.com>"]
 edition = "2018"
 
 [dependencies]
-tokio = { version = "0.2.22", features = ["time"] }
+tokio = { version = "0.3.2", features = ["time"] }
 web3 = "0.11.0"
-futures = { version = "0.3.5", features = ["compat"] }
+futures = { version = "0.3.7", features = ["compat"] }
 types = { path = "../../consensus/types"}
 serde_json = "1.0.58"
 deposit_contract = { path = "../../common/deposit_contract"}