[ingvarch]

What changes

Three ways to see and act on tasks and jobs without going one screen at a
time.

• m on a job opens its meta as keys and values, in the job's own namespace;
  c copies the value under the cursor. A job without meta says it has none.
• :tasks lists every task of every allocation of the namespace in one
  request: job, namespace, group, task, allocation, client, state, restarts,
  started, finished and uptime, colored by state like the other lists. A row
  has the keys of a task: logs, stderr, events, the events of its allocation,
  files, shell, restart, signal and run a command, each in the allocation's
  own namespace. The tasks screen of one allocation gets the Finished and
  Uptime columns too; Uptime sorts by length, not as text.
• ctrl+x on a running task asks for a command on the line at the top, runs
  it through /bin/sh -c without a terminal, and opens what it wrote to
  stdout and stderr as a text screen, with the exit code in the title: filter,
  find, copy, save and sideways scroll work on it as on a log. A command still
  running after 10 s is stopped and the status line says so. Only the last
  1 MiB of what it printed is kept, and the title says when it was cut. It is a
  write, hidden in read-only mode, like the shell.

Found and fixed along the way, in its own commit: G goes to the bottom of a
list, so a Group column offered shift-g to sort by it and pressing it
scrolled instead (:scaling, the groups of a deployment, now :tasks). No
column takes G now, and R stays with restarts, like N, A, S and P.
The save name of a long text is cut to 100 characters, so saving the output of
a long command does not fail on the length of the file name.

Closes #115
Closes #105
Closes #114

Checklist

• The test for this change was written first and failed
• make check is green
• The title is a conventional commit: feat(ui): ..., fix(nomad): ...