Add beacon.watch (#3362)

> This is currently a WIP and all features are subject to alteration or removal at any time.

## Overview

The successor to #2873.

Contains the backbone of `beacon.watch` including syncing code, the initial API, and several core database tables.

See `watch/README.md` for more information, requirements and usage.

watch/src/cli.rs

@@ -0,0 +1,55 @@
+use crate::{config::Config, logger, server, updater};
+use clap::{App, Arg};
+use tokio::sync::oneshot;
+
+pub const SERVE: &str = "serve";
+pub const RUN_UPDATER: &str = "run-updater";
+pub const CONFIG: &str = "config";
+
+fn run_updater<'a, 'b>() -> App<'a, 'b> {
+    App::new(RUN_UPDATER).setting(clap::AppSettings::ColoredHelp)
+}
+
+fn serve<'a, 'b>() -> App<'a, 'b> {
+    App::new(SERVE).setting(clap::AppSettings::ColoredHelp)
+}
+
+pub fn app<'a, 'b>() -> App<'a, 'b> {
+    App::new("beacon_watch_daemon")
+        .author("Sigma Prime <contact@sigmaprime.io>")
+        .setting(clap::AppSettings::ColoredHelp)
+        .arg(
+            Arg::with_name(CONFIG)
+                .long(CONFIG)
+                .value_name("PATH_TO_CONFIG")
+                .help("Path to configuration file")
+                .takes_value(true)
+                .global(true),
+        )
+        .subcommand(run_updater())
+        .subcommand(serve())
+}
+
+pub async fn run() -> Result<(), String> {
+    let matches = app().get_matches();
+
+    let config = match matches.value_of(CONFIG) {
+        Some(path) => Config::load_from_file(path.to_string())?,
+        None => Config::default(),
+    };
+
+    logger::init_logger(&config.log_level);
+
+    match matches.subcommand() {
+        (RUN_UPDATER, Some(_)) => updater::run_updater(config)
+            .await
+            .map_err(|e| format!("Failure: {:?}", e)),
+        (SERVE, Some(_)) => {
+            let (_shutdown_tx, shutdown_rx) = oneshot::channel();
+            server::serve(config, shutdown_rx)
+                .await
+                .map_err(|e| format!("Failure: {:?}", e))
+        }
+        _ => Err("Unsupported subcommand. See --help".into()),
+    }
+}