`Keyboard Shortcuts` tab: Consider a way to implement subsections in keystroke menu

[nexushoratio]

Recently we moved some keys around in the Feed menu so that destructive items, like toggle and nav+toggle, were towards the end and social keys (like, share, repost, send) were higher up. And we already have a policy about trying to have have read-only keys (next, activate, etc), near the top.

And that got me thinking: What about a way to provide a section separator in the key menu? Something like:

[
  {seq: ..., desc: ..., func: ...},
  {desc: 'Social actions'},
  {....},
];

And that would just result in a table row with no highlighting, just the description text.

• [ ] #185

[nexushoratio]

Idea: With #185, we are looking at allowing rows to have their own way of styling, via some sort of render() callback. We use that to do the styling for the major section headers, but also subsections as described here.