v1.0.407

Let alert jobs declare settings the owner can edit

A job can list the numbers it checks against (trip lines, targets, reference
rates) in each report. The Alerts page then shows Edit settings on the open
alert: the form replaces the checks in place, Done lists every change old →
new in a confirm dialog, and saving runs the job again so the new lines show
right away.

• Engine: validates the settings list, keeps the owner's values across
  reports, and drops a value once the job stops declaring it or narrows its
  range. PUT /api/alerts/sources/:id/settings now takes values as well as
  emails; a bad value is a readable 400 and saves nothing.
• Runner: hands the owner's values to every run in DOCVAULT_ALERT_SETTINGS,
  so a job needs no extra API call.
• Kit: setting(source, key) returns the value in effect, so a dashboard's
  lines move with the setting.
• docvault-health and overdue-invoices declare their thresholds as settings;
  their dashboard lines, colors and advice text follow them.