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>

testing/ef_tests/src/cases/bls_verify_msg.rs

@@ -1,14 +1,14 @@
 use super::*;
 use crate::case_result::compare_result;
 use crate::cases::common::BlsCase;
-use bls::{PublicKey, Signature, SignatureBytes};
+use bls::{PublicKeyBytes, Signature, SignatureBytes};
 use serde_derive::Deserialize;
 use std::convert::TryInto;
 use types::Hash256;
 
 #[derive(Debug, Clone, Deserialize)]
 pub struct BlsVerifyInput {
-    pub pubkey: PublicKey,
+    pub pubkey: PublicKeyBytes,
     pub message: String,
     pub signature: SignatureBytes,
 }
@@ -28,8 +28,9 @@ impl Case for BlsVerify {
 
         let signature_ok = (&self.input.signature)
             .try_into()
-            .map(|signature: Signature| {
-                signature.verify(&self.input.pubkey, Hash256::from_slice(&message))
+            .and_then(|signature: Signature| {
+                let pk = self.input.pubkey.decompress()?;
+                Ok(signature.verify(&pk, Hash256::from_slice(&message)))
             })
             .unwrap_or(false);