Implement standard eth2.0 API (#1569)

- Resolves #1550
- Resolves #824
- Resolves #825
- Resolves #1131
- Resolves #1411
- Resolves #1256
- Resolve #1177

- Includes the `ShufflingId` struct initially defined in #1492. That PR is now closed and the changes are included here, with significant bug fixes.
- Implement the https://github.com/ethereum/eth2.0-APIs in a new `http_api` crate using `warp`. This replaces the `rest_api` crate.
- Add a new `common/eth2` crate which provides a wrapper around `reqwest`, providing the HTTP client that is used by the validator client and for testing. This replaces the `common/remote_beacon_node` crate.
- Create a `http_metrics` crate which is a dedicated server for Prometheus metrics (they are no longer served on the same port as the REST API). We now have flags for `--metrics`, `--metrics-address`, etc.
- Allow the `subnet_id` to be an optional parameter for `VerifiedUnaggregatedAttestation::verify`. This means it does not need to be provided unnecessarily by the validator client.
- Move `fn map_attestation_committee` in `mod beacon_chain::attestation_verification` to a new `fn with_committee_cache` on the `BeaconChain` so the same cache can be used for obtaining validator duties.
- Add some other helpers to `BeaconChain` to assist with common API duties (e.g., `block_root_at_slot`, `head_beacon_block_root`).
- Change the `NaiveAggregationPool` so it can index attestations by `hash_tree_root(attestation.data)`. This is a requirement of the API.
- Add functions to `BeaconChainHarness` to allow it to create slashings and exits.
- Allow for `eth1::Eth1NetworkId` to go to/from a `String`.
- Add functions to the `OperationPool` to allow getting all objects in the pool.
- Add function to `BeaconState` to check if a committee cache is initialized.
- Fix bug where `seconds_per_eth1_block` was not transferring over from `YamlConfig` to `ChainSpec`.
- Add the `deposit_contract_address` to `YamlConfig` and `ChainSpec`. We needed to be able to return it in an API response.
- Change some uses of serde `serialize_with` and `deserialize_with` to a single use of `with` (code quality).
- Impl `Display` and `FromStr` for several BLS fields.
- Check for clock discrepancy when VC polls BN for sync state (with +/- 1 slot tolerance). This is not intended to be comprehensive, it was just easy to do.

- See #1434 for a per-endpoint overview.
- Seeking clarity here: https://github.com/ethereum/eth2.0-APIs/issues/75

- [x] Add docs for prom port to close #1256
- [x] Follow up on this #1177
- [x] ~~Follow up with #1424~~ Will fix in future PR.
- [x] Follow up with #1411
- [x] ~~Follow up with  #1260~~ Will fix in future PR.
- [x] Add quotes to all integers.
- [x] Remove `rest_types`
- [x] Address missing beacon block error. (#1629)
- [x] ~~Add tests for lighthouse/peers endpoints~~ Wontfix
- [x] ~~Follow up with validator status proposal~~ Tracked in #1434
- [x] Unify graffiti structs
- [x] ~~Start server when waiting for genesis?~~ Will fix in future PR.
- [x] TODO in http_api tests
- [x] Move lighthouse endpoints off /eth/v1
- [x] Update docs to link to standard

- ~~Blocked on #1586~~

Co-authored-by: Michael Sproul <michael@sigmaprime.io>

beacon_node/src/lib.rs

@@ -71,7 +71,6 @@ impl<E: EthSpec> ProductionBeaconNode<E> {
         context: RuntimeContext<E>,
         mut client_config: ClientConfig,
     ) -> Result<Self, String> {
-        let http_eth2_config = context.eth2_config().clone();
         let spec = context.eth2_config().spec.clone();
         let client_config_1 = client_config.clone();
         let client_genesis = client_config.genesis.clone();
@@ -118,26 +117,22 @@ impl<E: EthSpec> ProductionBeaconNode<E> {
             builder.no_eth1_backend()?
         };
 
-        let (builder, events) = builder
+        let (builder, _events) = builder
             .system_time_slot_clock()?
             .tee_event_handler(client_config.websocket_server.clone())?;
 
         // Inject the executor into the discv5 network config.
         client_config.network.discv5_config.executor = Some(Box::new(executor));
 
-        let builder = builder
+        builder
             .build_beacon_chain()?
             .network(&client_config.network)
             .await?
-            .notifier()?;
-
-        let builder = if client_config.rest_api.enabled {
-            builder.http_server(&client_config, &http_eth2_config, events)?
-        } else {
-            builder
-        };
-
-        Ok(Self(builder.build()))
+            .notifier()?
+            .http_api_config(client_config.http_api.clone())
+            .http_metrics_config(client_config.http_metrics.clone())
+            .build()
+            .map(Self)
     }
 
     pub fn into_inner(self) -> ProductionClient<E> {