[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/src/lib.rs

@@ -0,0 +1,34 @@
+mod cli;
+
+use clap::ArgMatches;
+use client::Client;
+use environment::Environment;
+use slog::info;
+use types::EthSpec;
+
+pub use cli::cli_app;
+
+pub fn run<E: EthSpec>(
+    environment: &mut Environment<E>,
+    matches: &ArgMatches,
+) -> Result<(), String> {
+    let context = environment.core_context();
+    let exit = context.executor.exit();
+
+    info!(
+        context.log(),
+        "Starting remote signer";
+    );
+
+    let client = environment
+        .runtime()
+        .block_on(Client::new(context, matches))
+        .map_err(|e| format!("Failed to init Rest API: {}", e))?;
+
+    environment.runtime().spawn(async move {
+        exit.await;
+        drop(client);
+    });
+
+    Ok(())
+}