Node Health warnings (#5951)

* Health endpoint.

* Asynchronous health endpoint.

* Configure time api URL via CLI.

* Tests for TimeChecker.

* Health indication on Status page.

* Adding status indication to tab titles.

* Add status to ParityBar.

* Fixing lints.

* Add health status on SyncWarning.

* Fix health URL for embed.

* Nicer messages.

* Fix tests.

* Fixing JS tests.

* NTP time sync (#5956)

* use NTP to check time drift

* update time module documentation

* replace time_api flag with ntp_server

* fix TimeChecker tests

* fix ntp-server flag usage

* hide status tooltip if there's no message to show

* remove TimeProvider trait

* use Cell in FakeNtp test trait

* share fetch client and ntp client cpu pool

* Add documentation to public method.

* Removing peer count from status.

* Remove unknown upgrade status.

* Send two time requests at the time.

* Revert "Send two time requests at the time."

This reverts commit f7b754b1155076a5a5d8fdafa022801fae324452.

* Defer reporting time synchronization issues.

* Fix tests.

* Fix linting.

util/fetch/src/client.rs

@@ -126,6 +126,11 @@ impl Client {
 		*self.client.write() = (time::Instant::now(), client.clone());
 		Ok(client)
 	}
+
+	/// Returns a handle to underlying CpuPool of this client.
+	pub fn pool(&self) -> CpuPool {
+		self.pool.clone()
+	}
 }
 
 impl Fetch for Client {
@@ -204,6 +209,15 @@ pub enum Error {
 	Aborted,
 }
 
+impl fmt::Display for Error {
+	fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+		match *self {
+			Error::Aborted => write!(fmt, "The request has been aborted."),
+			Error::Fetch(ref err) => write!(fmt, "{}", err),
+		}
+	}
+}
+
 impl From<reqwest::Error> for Error {
 	fn from(error: reqwest::Error) -> Self {
 		Error::Fetch(error)