* Implement public helpers for querying header info
* Update `best_header` when importing headers
* Add BestHeader to GenesisConfig
* Define extra types for Millau primitives
* Start implementing runtime APIs in Millau runtime
* Add helper for getting headers which require a justification
* Add runtime API for getting headers requiring a justification
* Reword `expect()` proof for valid authority sets
* Fix typo
* Clean up Hasher comment
* Add the Call Dispatch Pallet back to the Millau runtime
* Use types from Rialto in bridge pallet config
* Use the Rialto runtime APIS in the Millau runtime
* Include Millau bridge instance in Rialto runtime
* Add missing doc comment
* Use one storage function for setting and clearing `RequiresJustification`
* Remove TODO comments
Svyatoslav Nikolsky