* Stop passing raw encoded justifications to pallet API
By having the API accept a struct-ified justification we are able to
better utilize the justifications fields for weight calculations.
* Update relayer code to use decoded justifications
* Add justification to `expect()` statement
* Fix some imports
* Make justification wrapper contain decoded justification
* Rename some fields
* Get rid of warnings
* Appease Clippy
* Only decode justification once at init time
* Remove unnecessary method
* Remove justification wrapper
This became kinda unnecessary since we could implement the FinalityProof
trait on GrandpaJustification directly.
Svyatoslav Nikolsky