Move pool maintainance to a background task. (#1236)

* Move pool maintainance to a background task.

* Remove commented code.

* Add issue number to TODOs

* Fix warnings and tests.

substrate/srml/support/src/lib.rs

@@ -30,7 +30,6 @@ pub extern crate sr_primitives as runtime_primitives;
 extern crate srml_metadata;
 
 extern crate mashup;
-
 #[macro_use]
 extern crate srml_support_procedural;