journal/exhibit: add a margin on the bottom
journal/exhibit: add a margin on the bottom

If we leave it to 0, then the content above comes too close to the
footer, making it feel as if there is some hidden content that remains
hidden under the footer that we cannot scroll down to. Adding a
sufficient 'buffer' region of nothingness removes this feeling,
aesthetically.

listx/pf,listx/pf