Clean up the basic-authorship crate (#3206)

* Switch consensus-common to new futures

* Fix tests

* More tests fixing

* Make Proposer, OnSlot and SyncOracle mut

* Make the Environment mut as well

* Fix test

* Fix Babe tests

* Babe fixes

* Fix CLI service tests

* Fix Babe tests

* Remove unnecessary trait bound

* Inline the code of BlockBuilder and AuthoringApi

* Remove warning lint

* Bounds simplification

* Imports simplification

* Don't panic on bad generated block

* Code style

* Add doc example

* Remove dependency on aura

* Order dependencies alphabetically

* Minor style