Implement freezer database (#508)

* Implement freezer database for state vectors

* Improve BeaconState safe accessors

And fix a bug in the compact committees accessor.

* Banish dodgy type bounds back to gRPC

* Clean up

* Switch to exclusive end points in chunked vec

* Cleaning up and start of tests

* Randao fix, more tests

* Fix unsightly hack

* Resolve test FIXMEs

* Config file support

* More clean-ups, migrator beginnings

* Finish migrator, integrate into BeaconChain

* Fixups

* Fix store tests

* Fix BeaconChain tests

* Fix LMD GHOST tests

* Address review comments, delete 'static bounds

* Cargo format

* Address review comments

* Fix LMD ghost tests

* Update to spec v0.9.0

* Update to v0.9.1

* Bump spec tags for v0.9.1

* Formatting, fix CI failures

* Resolve accidental KeyPair merge conflict

* Document new BeaconState functions

* Fix incorrect cache drops in `advance_caches`

* Update fork choice for v0.9.1

* Clean up some FIXMEs

* Fix a few docs/logs

* Update for new builder paradigm, spec changes

* Freezer DB integration into BeaconNode

* Cleaning up

* This works, clean it up

* Cleanups

* Fix and improve store tests

* Refine store test

* Delete unused beacon_chain_builder.rs

* Fix CLI

* Store state at split slot in hot database

* Make fork choice lookup fast again

* Store freezer DB split slot in the database

* Handle potential div by 0 in chunked_vector

* Exclude committee caches from freezer DB

* Remove FIXME about long-running test

eth2/types/src/chain_spec.rs

@@ -241,7 +241,7 @@ impl ChainSpec {
 
     /// Ethereum Foundation minimal spec, as defined here:
     ///
-    /// https://github.com/ethereum/eth2.0-specs/blob/v0.8.1/configs/constant_presets/minimal.yaml
+    /// https://github.com/ethereum/eth2.0-specs/blob/v0.9.1/configs/minimal.yaml
     ///
     /// Spec v0.9.1
     pub fn minimal() -> Self {
@@ -249,9 +249,11 @@ impl ChainSpec {
         let boot_nodes = vec![];
 
         Self {
+            max_committees_per_slot: 4,
             target_committee_size: 4,
             shuffle_round_count: 10,
             min_genesis_active_validator_count: 64,
+            milliseconds_per_slot: 6_000,
             network_id: 2, // lighthouse testnet network id
             boot_nodes,
             eth1_follow_distance: 16,