Realized unrealized experimentation (#3322)

## Issue Addressed

Add a flag that optionally enables unrealized vote tracking.  Would like to test out on testnets and benchmark differences in methods of vote tracking. This PR includes a DB schema upgrade to enable to new vote tracking style.


Co-authored-by: realbigsean <sean@sigmaprime.io>
Co-authored-by: Paul Hauner <paul@paulhauner.com>
Co-authored-by: sean <seananderson33@gmail.com>
Co-authored-by: Mac L <mjladson@pm.me>

beacon_node/src/cli.rs

@@ -708,4 +708,12 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                 .default_value("250")
                 .takes_value(true)
         )
+        .arg(
+            Arg::with_name("count-unrealized")
+                .long("count-unrealized")
+                .hidden(true)
+                .help("**EXPERIMENTAL** Enables an alternative, potentially more performant FFG \
+                    vote tracking method.")
+                .takes_value(false)
+        )
 }

beacon_node/src/config.rs

@@ -630,6 +630,10 @@ pub fn get_config<E: EthSpec>(
         client_config.chain.fork_choice_before_proposal_timeout_ms = timeout;
     }
 
+    if cli_args.is_present("count-unrealized") {
+        client_config.chain.count_unrealized = true;
+    }
+
     Ok(client_config)
 }