fix(light-rpc): Make light_sync generic (#10238)

* fix(light-rpc): Make `light_sync` generic

The motivation behind this change is to easily mock `light-sync` to make it possible to enable `rpc-integration` tests
for the light-client.

Currently the `rpc's` requires the concrete type `sync::LightSync` which makes it very hard to do so

* fix(bad merge)

parity/light_helpers/epoch_fetch.rs

@@ -18,7 +18,7 @@ use std::sync::{Arc, Weak};
 
 use ethcore::engines::{EthEngine, StateDependentProof};
 use ethcore::machine::EthereumMachine;
-use sync::LightSync;
+use sync::{LightSync, LightNetworkDispatcher};
 use types::encoded;
 use types::header::Header;
 use types::receipt::Receipt;

parity/light_helpers/queue_cull.rs

@@ -20,7 +20,7 @@ use std::sync::Arc;
 use std::time::Duration;
 
 use ethcore::client::ClientIoMessage;
-use sync::LightSync;
+use sync::{LightSync, LightNetworkDispatcher};
 use io::{IoContext, IoHandler, TimerToken};
 
 use light::client::LightChainClient;