Say what each change is waiting for in the list

Say what each change is waiting for in the list

A change spends most of its life in states "open" cannot describe: held for a
maintainer to allow CI, running its checks, failed, waiting for a reviewer,
conflicting with its base. The list now says which of those it is, in one
column, with a tooltip that explains the label.

The answer comes from facts a list can afford: the approvals it already counts,
one batched run-queue query for every head on the page, the contributor
allowance (one ref listing, not one per row), and — only for a change that would
otherwise read as ready — whether it still merges into its base. The full
landing plan stays on the detail page.

The rest of the row follows the issue list: the author and opening moved under
the title, the comment count sits at the end of that line, and the last column
is "Updated", the newest commit over the request's directory. The list sorts by
it. The separate Author, Approvals and Age columns are gone.

Closes #194