[Remote signer] Fold signer into Lighthouse repository (#1852)

The remote signer relies on the `types` and `crypto/bls` crates from Lighthouse. Moreover, a number of tests of the remote signer consumption of LH leverages this very signer, making any important update a potential dependency nightmare.

Co-authored-by: Paul Hauner <paul@paulhauner.com>

remote_signer/client/src/config.rs

@@ -0,0 +1,20 @@
+use serde::{Deserialize, Serialize};
+use std::net::Ipv4Addr;
+
+/// HTTP REST API Configuration
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Config {
+    /// The IPv4 address the REST API HTTP server will listen on.
+    pub listen_address: Ipv4Addr,
+    /// The port the REST API HTTP server will listen on.
+    pub port: u16,
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Config {
+            listen_address: Ipv4Addr::new(127, 0, 0, 1),
+            port: 9000,
+        }
+    }
+}