⌨️ J-Editor: Look at recent updates to Slate & potentially update to @latest

[robin-macpherson]

(Related to #783)

What

Our current versions of Slate are:

"slate": "^0.72.3",
"slate-history": "^0.66.0",
"slate-hyperscript": "^0.67.0",
"slate-react": "^0.72.7",

In the past we became very hesitant to keep our version up-to-date with each release because there were frequently new bugs introduced and then roll-backs in subsequent versions, but at this point there have been quite a lot of new versions. Current versions are:

"slate": "0.88.1",
"slate-history": "0.86.0",
"slate-hyperscript": "^0.77.0",
"slate-react": "0.88.2",

Given this, hopefully on average there have been a lot of improvements and I'm thinking we should try updating and do some smoke testing and also see if our last remaining bugs are fixed.