fix(client): show "present" string if end date is not entered, also add to i18n locales

fix #653

client/public/locales/en/common.json

@@ -15,6 +15,9 @@
   "markdown": {
     "help-text": "This section supports <1>markdown</1> formatting."
   },
+  "date": {
+    "present": "Present"
+  },
   "subtitle": "A free and open source resume builder.",
   "title": "Reactive Resume",
   "toast": {