feat: task checklist improvements (#797)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/797
Co-authored-by: konrad <k@knt.li>
Co-committed-by: konrad <k@knt.li>

src/i18n/lang/en.json

@@ -499,6 +499,8 @@
     "doneSuccess": "The task was successfully marked as done.",
     "undoneSuccess": "The task was successfully un-marked as done.",
     "openDetail": "Open task detail view",
+    "checklistTotal": "{checked} of {total} tasks",
+    "checklistAllDone": "{total} tasks",
     "show": {
       "titleCurrent": "Current Tasks",
       "titleDates": "Tasks from {from} until {to}",