Identity system for Subnets and Root-validators (#191)

* Start identity pallet

* Rename identity to registry, import some FRAME types for identity fields

* Add IdentityUpdated event

* Finish set_identity and clear_identity extrinsic implementations

* Add types to handle storage of identities on-chain

* Remove unused import

* Add benchmarking and WeightInfo for pallet_registry

* Add is_subnet_owner util function, implement can_register to only allow identities for root validators and subnet owners

* Use is_hotkey_registered_on_network over get_axon_info for CanRegisterIdentity

* Allow specification of hotkey-coldkey pair when registering identity

* Add Raw33 -> Raw64 fields for larger identity fields

* Fix errors caused by Raw type bounds at 32

* Fix set_identity using wrong address when inserting data into storage

* Update clear_identity to allow for identified argument