Altair consensus changes and refactors (#2279)

## Proposed Changes

Implement the consensus changes necessary for the upcoming Altair hard fork.

## Additional Info

This is quite a heavy refactor, with pivotal types like the `BeaconState` and `BeaconBlock` changing from structs to enums. This ripples through the whole codebase with field accesses changing to methods, e.g. `state.slot` => `state.slot()`.


Co-authored-by: realbigsean <seananderson33@gmail.com>

beacon_node/operation_pool/Cargo.toml

@@ -21,3 +21,5 @@ store = { path = "../store" }
 
 [dev-dependencies]
 rand = "0.7.3"
+lazy_static = "1.4.0"
+beacon_chain =  { path = "../beacon_chain" }