Feed previews: consistent title size and more spacing between items

In the main feed, when a note (or any item) shows just a title with no visible description, the title renders larger. This makes it look like a different kind of item than it is, and it's hard to tell items apart at a glance.

Wanted

• Title size should be consistent across all notes and encrypted items, whether or not a description is shown.
• Increase the vertical spacing between items in the feed; it's currently a bit tight. Roughly double the spacing between each item box.