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>

lcli/src/new_testnet.rs

@@ -51,11 +51,11 @@ pub fn run<T: EthSpec>(matches: &ArgMatches) -> Result<(), String> {
         spec.genesis_fork_version = v;
     }
 
-    let testnet: Eth2TestnetConfig<T> = Eth2TestnetConfig {
+    let testnet = Eth2TestnetConfig {
         deposit_contract_address: format!("{:?}", deposit_contract_address),
         deposit_contract_deploy_block,
         boot_enr: Some(vec![]),
-        genesis_state: None,
+        genesis_state_bytes: None,
         yaml_config: Some(YamlConfig::from_spec::<T>(&spec)),
     };