Rewrite the BasiQueue using channels (#1327)

* use channels to implement basic import queue

* async justification import

* better conditional for is_done in tests

* reword the test for presence of link

* fix conditional

* trace instead of panic when no link present

* reword expectations when sending to importers

* fix

* debug justification import error

* update expectations

* use NumberFor

* nits

* add general description

* move error handling into closure

substrate/node-template/src/service.rs

@@ -84,8 +84,6 @@ construct_service_factory! {
 			{ |config, executor| <LightComponents<Factory>>::new(config, executor) },
 		FullImportQueue = AuraImportQueue<
 			Self::Block,
-			FullClient<Self>,
-			NothingExtra,
 		>
 			{ |config: &mut FactoryFullConfiguration<Self> , client: Arc<FullClient<Self>>|
 				import_queue(
@@ -99,8 +97,6 @@ construct_service_factory! {
 			},
 		LightImportQueue = AuraImportQueue<
 			Self::Block,
-			LightClient<Self>,
-			NothingExtra,
 		>
 			{ |config: &mut FactoryFullConfiguration<Self>, client: Arc<LightClient<Self>>|
 				import_queue(