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.

dapps/src/handlers/content.rs

@@ -39,10 +39,6 @@ impl ContentHandler {
 		Self::new(StatusCode::Ok, content, mimetype)
 	}
 
-	pub fn not_found(content: String, mimetype: Mime) -> Self {
-		Self::new(StatusCode::NotFound, content, mimetype)
-	}
-
 	pub fn html(code: StatusCode, content: String, embeddable_on: Option<(String, u16)>) -> Self {
 		Self::new_embeddable(code, content, mime!(Text/Html), embeddable_on)
 	}