Introduce timeHelpers service

Instead of the fuzzyTime filter (and without abusing it)
introducing this service which generates the fuzzyTimeString
(as message) and the next time the fuzzyTimeString should be
updated in seconds (as updateAt) from a given datetime object..

h/static/scripts/helpers/time-helpers.coffee

+createTimeHelpers = ->
+  timestamp: (date) ->
+    return {message: '', updateAt: 5} if not date
+    delta = Math.round((+new Date - new Date(date)) / 1000)
+
+    minute = 60
+    hour = minute * 60
+    day = hour * 24
+    month = day * 30
+    year = day * 365
+
+    if (delta < 30)
+      message = 'moments ago'
+      updateAt = 30 - delta
+    else if (delta < minute)
+      message = delta + ' seconds ago'
+      updateAt = 1
+     else if (delta < 2 * minute)
+      message = 'a minute ago'
+      updateAt = 2*minute - delta
+     else if (delta < hour)
+      message = Math.floor(delta / minute) + ' minutes ago'
+      updateAt = minute
+     else if (Math.floor(delta / hour) == 1)
+      message = '1 hour ago'
+      updateAt = hour
+     else if (delta < day)
+      message = Math.floor(delta / hour) + ' hours ago'
+      updateAt = hour
+     else if (delta < day * 2)
+      message = 'yesterday'
+      updateAt = 2*day - delta
+     else if (delta < month)
+      message = Math.round(delta / day) + ' days ago'
+      updateAt = day
+     else if (delta < year)
+      message = Math.round(delta / month) + ' months ago'
+      updateAt = month
+     else
+      message = Math.round(delta / year) + ' years ago'
+      updateAt= year
+
+    message: message
+    updateAt: updateAt
+
+angular.module('h.helpers')
+.factory('timeHelpers', createTimeHelpers)
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