Update to spec v1.0.0-rc.0 and BLSv4 (#1765)

## Issue Addressed

Closes #1504 
Closes #1505
Replaces #1703
Closes #1707

## Proposed Changes

* Update BLST and Milagro to versions compatible with BLSv4 spec
* Update Lighthouse to spec v1.0.0-rc.0, and update EF test vectors
* Use the v1.0.0 constants for `MainnetEthSpec`.
* Rename `InteropEthSpec` -> `V012LegacyEthSpec`
    * Change all constants to suit the mainnet `v0.12.3` specification (i.e., Medalla).
* Deprecate the `--spec` flag for the `lighthouse` binary
    * This value is now obtained from the `config_name` field of the `YamlConfig`.
        * Built in testnet YAML files have been updated.
    * Ignore the `--spec` value, if supplied, log a warning that it will be deprecated
    * `lcli` still has the spec flag, that's fine because it's dev tooling.
* Remove the `E: EthSpec` from `YamlConfig`
    * This means we need to deser the genesis `BeaconState` on-demand, but this is fine.
* Swap the old "minimal", "mainnet" strings over to the new `EthSpecId` enum.
* Always require a `CONFIG_NAME` field in `YamlConfig` (it used to have a default).

## Additional Info

Lots of breaking changes, do not merge! ~~We will likely need a Lighthouse v0.4.0 branch, and possibly a long-term v0.3.0 branch to keep Medalla alive~~.

Co-authored-by: Kirk Baird <baird.k@outlook.com>
Co-authored-by: Paul Hauner <paul@paulhauner.com>

boot_node/src/config.rs

@@ -5,7 +5,6 @@ use eth2_libp2p::{
     discovery::{create_enr_builder_from_config, use_or_load_enr},
     load_private_key, CombinedKeyExt, NetworkConfig,
 };
-use eth2_testnet_config::Eth2TestnetConfig;
 use ssz::Encode;
 use std::convert::TryFrom;
 use std::marker::PhantomData;
@@ -30,7 +29,7 @@ impl<T: EthSpec> TryFrom<&ArgMatches<'_>> for BootNodeConfig<T> {
         let data_dir = get_data_dir(matches);
 
         // Try and grab testnet config from input CLI params
-        let eth2_testnet_config: Option<Eth2TestnetConfig<T>> = {
+        let eth2_testnet_config = {
             if matches.is_present("testnet") {
                 Some(get_eth2_testnet_config(&matches)?)
             } else {
@@ -95,7 +94,9 @@ impl<T: EthSpec> TryFrom<&ArgMatches<'_>> for BootNodeConfig<T> {
                 .apply_to_chain_spec::<T>(&T::default_spec())
                 .ok_or_else(|| "The loaded config is not compatible with the current spec")?;
 
-            if let Some(genesis_state) = config.genesis_state.as_ref() {
+            if config.beacon_state_is_known() {
+                let genesis_state = config.beacon_state::<T>()?;
+
                 slog::info!(logger, "Genesis state found"; "root" => genesis_state.canonical_root().to_string());
                 let enr_fork = spec.enr_fork_id(
                     types::Slot::from(0u64),