Move authorities interface from Core to consensus (#1412)

* Move authorities interface from Core to consensus

f

* notify all caches of block insert + create with up-to-date best_fin

* merged authorities_are_cached from light_grandpa_import2

* Add ProvideCache trait

* Create helper function for 'get_cache'

* Fix some formatting

* Bump impl version

* Resolve wasm conflicts

* Apply review comments

* Use try_for_each

* Move authorities interface from Core to consensus

f

* notify all caches of block insert + create with up-to-date best_fin

* merged authorities_are_cached from light_grandpa_import2

* Add ProvideCache trait

* Create helper function for 'get_cache'

* Fix some formatting

* Bump impl version

* Resolve wasm conflicts

* Apply review comments

* Use try_for_each

* Move authorities interface from Core to consensus

f

* notify all caches of block insert + create with up-to-date best_fin

* merged authorities_are_cached from light_grandpa_import2

* Add ProvideCache trait

* Create helper function for 'get_cache'

* Fix some formatting

* Bump impl version

* Resolve wasm conflicts

* Apply review comments

* Use try_for_each

* Increment impl_version

* Update lib.rs