1.6 feature merge

[marc-casperlabs]

This PR is a summary merge of every new feature and fix that has not made it to dev yet and is currently slated for a 1.6 release. Parts of the code have been reviewed already, but this does not apply to the entirety of the changes nor their combination.

The PR contains multiple larger changesets:

• The juliet crate and its integration into the node, forming the new base networking for the 1.6 release. There are some open TODOs, feel free to point them out, but follow-ups have been ticketed in most, if not all cases.
• EE changes:
  • Prunes withdraw keys post migration
  • Wasmi is updated to 0.13.2
  • Pruning is exposed as a new transform and could be found in the journal
  • Better error messages when trying to run Wasm with non-MVP opcodes
• Smaller fixes, expanded test coverage (e.g. around metrics) and utility features and refactorings have been added.

While the review may seem a little daunting, if focusing on a single aspect at once (EE, juliet, integration of juliet and misc changes) should make it more manageable.

History is preserved, keeping some features that never made it to mainline, thus the high number of commits, along with numerous merge commits of dev back into the branch for compatibility.

Closes #3941.

[Fraser999]

Mostly nitpicks and questions around todos being ticketed.

I skipped review of the juliet crate as I have already done that on the feature branch and I assume it hasn't changed since then.

We do still need to decide if the crate gets its own repo or not. If not, then points made in the previous review which should be addressed include:

• decide the crate's name
• specify edition = "2018" (or upgrade all manifests in the repo)
• add standard items to manifest's [package] section (especially the license field)
• update the README.md to include the standard blurb at the top and the license info
• add the crate to the casper-updater tool and publish_to_crates_io.sh

[rafal-ch]

Initial review

[rafal-ch]

There were some issue observed during manual run of the network_soundness.py (some or all nodes get stuck over time). It'll be good to resolve that before merging to dev in order not to break the nightly pipeline. Details have been discussed with @marc-casperlabs .

[cspramit]

timeline on or before Monday 9th @SaiProServ

[marc-casperlabs]

bors try

[casperlabs-bors-ng]

try

Build succeeded:

• continuous-integration/drone/push

[marc-casperlabs]

bors try

[casperlabs-bors-ng]

try

Merge conflict.

[marc-casperlabs]

bors try

[casperlabs-bors-ng]

try

Build succeeded:

• continuous-integration/drone/push

[marc-casperlabs]

Will be reopened cleanly in a separate PR.