Update beacon crate to spec v0.6.1 (#128)

* [WIP] Update all config and struct definitions

* [WIP] Utils function spec update I

* [WIP] Utils functions spec update II

* [WIP] Re-init beacon

Cherry-pick back old code rather than modifying it is easier to do -- as there are many changes.

* [WIP] Cherry-pick back all types

* [WIP] Cherry pick back all helpers

* [WIP] Cherry-pick back validator status helpers

* [WIP] Migrate back per epoch helpers

* [WIP] Cherry-pick justification and finalization

* [WIP] Redo crosslink and rewards

* [WIP] Cherry-pick back all per epoch operations

* [WIP]

* [WIP] Port back all operations

* Add state root verification

* [WIP] Fix warnings

* Finish fixing all warnings

* Add function to execute block

* Add back small config

* Add new test repo

* Update yamltests for the new format and pass those tests

* Check block state root in execute_block

* Add full tests

* Update tests

* Add back block builder

* Fix other crate compile

* Make beacon crate work again in no_std