layout: minor things that takes too much vertical space

Hey, just a couple of nits about excessive (IMHO) use of vertical space:

• In the homepage view, the Last update: ... line can be but on the top right, near the counter of number of versions, which also makes "logical" sense as they are both metadata
• In the dataset view, e.g., /graphs/columnar/, permalink does not need two full lines, in fact I think the link can just be the href of "permalink" as anchor and the anchor can be moved either to the top right. Or, even better, we could follow what seems to be common practice for links in documentation, that is of showing a section sign (§) when hovering on the dataset title, and put the permalink on it