Assignee field like Jira #2452 , in progress.

Add assignee popup title.

Thanks to xet7 !

i18n/en.i18n.json

@@ -751,5 +751,6 @@
   "accounts-allowUserDelete": "Allow users to self delete their account",
   "hide-minicard-label-text": "Hide minicard label text",
   "show-desktop-drag-handles": "Show desktop drag handles",
-  "assignee": "Assignee"
+  "assignee": "Assignee",
+  "cardAssigneesPopup-title": "Assignee"
 }