Server sent events (#1920)

## Issue Addressed

Resolves #1434 (this is the last major feature in the standard spec. There are only a couple of places we may be off-spec due to recent spec changes or ongoing discussion)
Partly addresses #1669
 
## Proposed Changes

- remove the websocket server
- remove the `TeeEventHandler` and `NullEventHandler` 
- add server sent events according to the eth2 API spec

## Additional Info

This is according to the currently unmerged PR here: https://github.com/ethereum/eth2.0-APIs/pull/117


Co-authored-by: realbigsean <seananderson33@gmail.com>

beacon_node/src/cli.rs

@@ -232,29 +232,6 @@ pub fn cli_app<'a, 'b>() -> App<'a, 'b> {
                     address of this server (e.g., http://localhost:5054).")
                 .takes_value(true),
         )
-        /* Websocket related arguments */
-        .arg(
-            Arg::with_name("ws")
-                .long("ws")
-                .help("Enable the websocket server. Disabled by default.")
-                .takes_value(false),
-        )
-        .arg(
-            Arg::with_name("ws-address")
-                .long("ws-address")
-                .value_name("ADDRESS")
-                .help("Set the listen address for the websocket server.")
-                .default_value("127.0.0.1")
-                .takes_value(true),
-        )
-        .arg(
-            Arg::with_name("ws-port")
-                .long("ws-port")
-                .value_name("PORT")
-                .help("Set the listen TCP port for the websocket server.")
-                .default_value("5053")
-                .takes_value(true),
-        )
 
         /*
          * Standard staking flags

beacon_node/src/config.rs

@@ -150,26 +150,6 @@ pub fn get_config<E: EthSpec>(
         );
     }
 
-    /*
-     * Websocket server
-     */
-
-    if cli_args.is_present("ws") {
-        client_config.websocket_server.enabled = true;
-    }
-
-    if let Some(address) = cli_args.value_of("ws-address") {
-        client_config.websocket_server.listen_address = address
-            .parse::<Ipv4Addr>()
-            .map_err(|_| "ws-address is not a valid IPv4 address.")?;
-    }
-
-    if let Some(port) = cli_args.value_of("ws-port") {
-        client_config.websocket_server.port = port
-            .parse::<u16>()
-            .map_err(|_| "ws-port is not a valid u16.")?;
-    }
-
     /*
      * Eth1
      */
@@ -250,7 +230,6 @@ pub fn get_config<E: EthSpec>(
             unused_port("udp").map_err(|e| format!("Failed to get port for discovery: {}", e))?;
         client_config.http_api.listen_port = 0;
         client_config.http_metrics.listen_port = 0;
-        client_config.websocket_server.port = 0;
     }
 
     /*

beacon_node/src/lib.rs

@@ -5,18 +5,16 @@ mod cli;
 mod config;
 
 pub use beacon_chain;
-pub use cli::cli_app;
-pub use client::{Client, ClientBuilder, ClientConfig, ClientGenesis};
-pub use config::{get_config, get_data_dir, get_eth2_testnet_config, set_network_config};
-pub use eth2_config::Eth2Config;
-
-use beacon_chain::events::TeeEventHandler;
 use beacon_chain::store::LevelDB;
 use beacon_chain::{
     builder::Witness, eth1_chain::CachingEth1Backend, slot_clock::SystemTimeSlotClock,
 };
 use clap::ArgMatches;
+pub use cli::cli_app;
+pub use client::{Client, ClientBuilder, ClientConfig, ClientGenesis};
+pub use config::{get_config, get_data_dir, get_eth2_testnet_config, set_network_config};
 use environment::RuntimeContext;
+pub use eth2_config::Eth2Config;
 use slasher::Slasher;
 use slog::{info, warn};
 use std::ops::{Deref, DerefMut};
@@ -24,16 +22,8 @@ use std::sync::Arc;
 use types::EthSpec;
 
 /// A type-alias to the tighten the definition of a production-intended `Client`.
-pub type ProductionClient<E> = Client<
-    Witness<
-        SystemTimeSlotClock,
-        CachingEth1Backend<E>,
-        E,
-        TeeEventHandler<E>,
-        LevelDB<E>,
-        LevelDB<E>,
-    >,
->;
+pub type ProductionClient<E> =
+    Client<Witness<SystemTimeSlotClock, CachingEth1Backend<E>, E, LevelDB<E>, LevelDB<E>>>;
 
 /// The beacon node `Client` that will be used in production.
 ///
@@ -121,9 +111,7 @@ impl<E: EthSpec> ProductionBeaconNode<E> {
             builder.no_eth1_backend()?
         };
 
-        let (builder, _events) = builder
-            .system_time_slot_clock()?
-            .tee_event_handler(client_config.websocket_server.clone())?;
+        let builder = builder.system_time_slot_clock()?;
 
         // Inject the executor into the discv5 network config.
         let discv5_executor = Discv5Executor(executor);