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>

consensus/fork_choice/src/fork_choice.rs

@@ -4,7 +4,7 @@ use proto_array::{Block as ProtoBlock, ProtoArrayForkChoice};
 use ssz_derive::{Decode, Encode};
 use types::{
     BeaconBlock, BeaconState, BeaconStateError, Checkpoint, Epoch, EthSpec, Hash256,
-    IndexedAttestation, Slot,
+    IndexedAttestation, RelativeEpoch, ShufflingId, Slot,
 };
 
 use crate::ForkChoiceStore;
@@ -240,10 +240,18 @@ where
     /// Instantiates `Self` from the genesis parameters.
     pub fn from_genesis(
         fc_store: T,
+        genesis_block_root: Hash256,
         genesis_block: &BeaconBlock<E>,
+        genesis_state: &BeaconState<E>,
     ) -> Result<Self, Error<T::Error>> {
         let finalized_block_slot = genesis_block.slot;
         let finalized_block_state_root = genesis_block.state_root;
+        let current_epoch_shuffling_id =
+            ShufflingId::new(genesis_block_root, genesis_state, RelativeEpoch::Current)
+                .map_err(Error::BeaconStateError)?;
+        let next_epoch_shuffling_id =
+            ShufflingId::new(genesis_block_root, genesis_state, RelativeEpoch::Next)
+                .map_err(Error::BeaconStateError)?;
 
         let proto_array = ProtoArrayForkChoice::new(
             finalized_block_slot,
@@ -251,6 +259,8 @@ where
             fc_store.justified_checkpoint().epoch,
             fc_store.finalized_checkpoint().epoch,
             fc_store.finalized_checkpoint().root,
+            current_epoch_shuffling_id,
+            next_epoch_shuffling_id,
         )?;
 
         Ok(Self {
@@ -534,6 +544,10 @@ where
             root: block_root,
             parent_root: Some(block.parent_root),
             target_root,
+            current_epoch_shuffling_id: ShufflingId::new(block_root, state, RelativeEpoch::Current)
+                .map_err(Error::BeaconStateError)?,
+            next_epoch_shuffling_id: ShufflingId::new(block_root, state, RelativeEpoch::Next)
+                .map_err(Error::BeaconStateError)?,
             state_root: block.state_root,
             justified_epoch: state.current_justified_checkpoint.epoch,
             finalized_epoch: state.finalized_checkpoint.epoch,