Integrate Approval Voting into Overseer / Service / GRANDPA (#2412)

* integrate approval voting into overseer

* expose public API and make keystore arc

* integrate overseer in service

* guide: `ApprovedAncestor` returns block number

* return block number along with hash from ApprovedAncestor

* introduce a voting rule for reporting on approval checking

* integrate the delay voting rule

* Rococo configuration

* fix compilation and add slack

* fix web-wasm build

* tweak parameterization

* migrate voting rules to asycn

* remove hack comment

polkadot/Cargo.lock

@@ -5851,6 +5851,7 @@ dependencies = [
  "polkadot-collator-protocol",
  "polkadot-network-bridge",
  "polkadot-node-collation-generation",
+ "polkadot-node-core-approval-voting",
  "polkadot-node-core-av-store",
  "polkadot-node-core-backing",
  "polkadot-node-core-bitfield-signing",
@@ -5883,6 +5884,7 @@ dependencies = [
  "sc-executor",
  "sc-finality-grandpa",
  "sc-finality-grandpa-warp-sync",
+ "sc-keystore",
  "sc-network",
  "sc-service",
  "sc-telemetry",