Port glitch-soc features to grouped notifications column

[ClearlyClaire]

#2782 introduces experimental notification grouping from upstream, but this is lacking glitch-soc features:

• notification cleanup
• collapsed posts/notifications (maybe we don't need it as much?)
• different link handling

[roycewilliams]

I'm testing the "group notifications" preview. I know this is a commingling of upstream and local changes, but the overall effect is that it eats significantly more vertical space per post, because:

A) it now treats the like / boost icon on the left as a separate column, forcing the rest of the content further right (and leaving a significant chunk of unused whitespace), and

B) it has its own, new, local sense of max display length, with no way to collapse/shrink the vertical space used (unlike the old method, which inherits the collapse/expand button and expand-or-not defaults from the general settings), and

C) it treats CWs oddly - it drops the un-hidden CW preamble entirely ... but then shows the text normally hidding by CW!

The overall effect is a tripling of vertical space used per notification, with no way to configure trade-offs.

The change in amount of screen real estate used vs empty is significant: