Keystone: Housekeeping: Upgrade slate

[Vultraz]

slate 0.50.0 completely redesigned the codebase and the upgrade is is apparently non-trivial. See https://github.com/ianstormtaylor/slate/blob/master/Changelog.md#0500--november-27-2019 for more info.

[jesstelford]

Yes! I've been meaning to look into this deeper.

The biggest hurdle I think we're going to face is any data-shape changes meaning existing sites may have to migrate their data somehow into the new format. I hope the changes are minimal.

[Vultraz]

Started working on this locally.

[Vultraz]

2510 (very WIP)

[stale[bot]]

It looks like there hasn't been any activity here in over 6 months. Sorry about that! We've flagged this issue for special attention. It wil be manually reviewed by maintainers, not automatically closed. If you have any additional information please leave us a comment. It really helps! Thank you for you contribution. :)

[acoreyj]

@JedWatson I saw somewhere a new field is being added that uses the new version of Slate, is there an ETA for that?

Thanks!