Cleaning up the rest of the API functions.

- Removed all unused imports
 - Fixed random compiler errors
 - Removed all of the 'sucess_response' helpers.
 - Enabled all of the API endpoints again, wrapping in 'into_boxfut'
 - Tidied up /metrics endpoint
 - Added a 'body_text' part to ResponseBuilder, mainly for the Prometheus /metrics endpoint
 - Cleaned up the unnecessary helpers::* imports, to be more explicit.

beacon_node/rest_api/src/validator.rs

@@ -1,11 +1,14 @@
-use crate::helpers::*;
+use crate::helpers::{
+    check_content_type_for_json, get_beacon_chain_from_request, get_logger_from_request,
+    parse_pubkey, publish_beacon_block_to_network,
+};
 use crate::response_builder::ResponseBuilder;
 use crate::{ApiError, ApiResult, BoxFut, UrlQuery};
 use beacon_chain::{BeaconChainTypes, BlockProcessingOutcome};
 use bls::{AggregateSignature, PublicKey, Signature};
 use futures::future::Future;
 use futures::stream::Stream;
-use hyper::{Body, Error, Request};
+use hyper::{Body, Request};
 use network::NetworkMessage;
 use parking_lot::RwLock;
 use serde::{Deserialize, Serialize};