Add recurring expense functionality (#263)

* code complete

* Smaller updates

* delete ambitious TODOs (add to PR)

* add transactionality to recurring expense creation

* Remove unnecessary `let`s

* Add default english labels to non-en-US translations

* Accept `es.json` translations

* add condition to ensure links are only modified when applicable

messages/ru-RU.json

@@ -137,6 +137,15 @@
         "label": "Получивший",
         "description": "Выберите участника, который получил этот доход."
       },
+      "recurrenceRule": {
+        "label": "Expense Recurrence",
+        "description": "Select how often the expense should repeat.",
+
+        "none": "None",
+        "daily": "Daily",
+        "weekly": "Weekly",
+        "monthly": "Monthly"
+      },
       "paidFor": {
         "title": "Участники",
         "description": "Выберите тех, между кем этот доход будет распределен."