Support displaying time in absolute format

This adds two config items: useAbsoluteTimeFormat (boolean) and
absoluteTimeFormatMinAge (string, number + unit ('d'|'h'|'m'|'s')).

When `useAbsoluteTimeFormat` is true, the Timeago component will display
absolute time if the time is at least `absoluteTimeFormatMinAge`
from now. If `longFormat` prop is true, the fully formatted time
is displayed. Otherwise, the format is determined by the `time` prop:
(1) if `time` is on the same day of now, display hour and minute;
(2) if `time` is in the same month of now, display day and hour;
(3) if `time` is in the same year of now, display month and day;
(4) otherwise, display year and month.

If it should display relative time, the format is the same as before.

src/services/date_utils/date_utils.js

@@ -6,10 +6,13 @@ export const WEEK = 7 * DAY
 export const MONTH = 30 * DAY
 export const YEAR = 365.25 * DAY
 
-export const relativeTime = (date, nowThreshold = 1) => {
+export const relativeTimeMs = (date) => {
   if (typeof date === 'string') date = Date.parse(date)
+  return Math.abs(Date.now() - date)
+}
+export const relativeTime = (date, nowThreshold = 1) => {
   const round = Date.now() > date ? Math.floor : Math.ceil
-  const d = Math.abs(Date.now() - date)
+  const d = relativeTimeMs(date)
   const r = { num: round(d / YEAR), key: 'time.unit.years' }
   if (d < nowThreshold * SECOND) {
     r.num = 0
@@ -57,3 +60,39 @@ export const secondsToUnit = (unit, amount) => {
     case 'days': return (1000 * amount) / DAY
   }
 }
+
+export const isSameYear = (a, b) => {
+  return a.getFullYear() === b.getFullYear()
+}
+
+export const isSameMonth = (a, b) => {
+  return a.getFullYear() === b.getFullYear() &&
+    a.getMonth() === b.getMonth()
+}
+
+export const isSameDay = (a, b) => {
+  return a.getFullYear() === b.getFullYear() &&
+    a.getMonth() === b.getMonth() &&
+    a.getDate() === b.getDate()
+}
+
+export const durationStrToMs = (str) => {
+  if (typeof str !== 'string') {
+    return 0
+  }
+
+  const unit = str.replace(/[0-9,.]+/, '')
+  const value = str.replace(/[^0-9,.]+/, '')
+  switch (unit) {
+    case 'd':
+      return value * DAY
+    case 'h':
+      return value * HOUR
+    case 'm':
+      return value * MINUTE
+    case 's':
+      return value * SECOND
+    default:
+      return 0
+  }
+}