Add an action to a year's memo

One of three shapes. A catalogue entry (catalogueKey, optional reductionPct within the entry's range, baseId when the entry applies to several bases). A base with the user's or Tally's own percentage (title, baseId, reductionPct, rationale). A typed estimate (title, scope, estimateKgCo2e, rationale). Core works out the estimate; a percentage outside a catalogue entry's range needs a rationale and makes the estimate a tally one. 404 ACTION_MEMO_NOT_FOUND; 400 VALIDATION_ERROR (the message says why). Requires org.edit_dashboard.