Merge remote-tracking branch 'origin/master' into...

Merge remote-tracking branch 'origin/master' into dp/make-CallExecutors-generic-over-hasher-and-rlpcodec

* origin/master: (26 commits)
  Contract runtime polishing (#601)
  WIP on chain heap (#639)
  Events to track extrinsic success (#640)
  Install llvm-tools-preview component (#643)
  fix wasm executor compile error (#631)
  random fixes (#638)
  Empty becomes (), reflecting convention (#637)
  Allow to build_upon skipped entries, but don't walk back (#635)
  Separate out staking module into balances and payment (#629)
  Update .gitlab-ci.yml (#633)
  Do not attempt to rustup if in CI. This is taken care of by the base (#621)
  Avoid need for ident strings in storage (#624)
  rename to panic_handler as panic_implementation is deprecated in nightly (#626)
  5 random fixes (#2) (#623)
  fix one typo in README (#627)
  Misspelled words (#625)
  Contracts: Per block gas limit (#506)
  Make sure to ban invalid transactions. (#615) (#620)
  Forward-port BFT fixes from v0.2 and restructure agreement cancelling (#619)
  Allow specifying listening multiaddresses (#577)
  ...