Add daysago formatter and extract common helper to reuse with indays formatter

app/javascript/helpers/date_helpers.js

@@ -0,0 +1,7 @@
+export function differenceInDays(fromDate, toDate) {
+  return Math.round(Math.abs((beginningOfDay(toDate) - beginningOfDay(fromDate)) / (1000 * 60 * 60 * 24)))
+}
+
+export function beginningOfDay(date) {
+  return new Date(date.getFullYear(), date.getMonth(), date.getDate())
+}