Merge branch 'master' into dp/fix/impl-MaybeEmpty-only-where-needed

* master:
  Revert "Install llvm-tools-preview component (#643)" (#644)
  Revert "fix wasm executor compile error (#631)" (#642)
  Fetch parity-common dependencies from crates (#617)
  limit retry count in OnDemand (#513)
  Minor refactor for staking module (#659)