Added full interpolation support to the i18n

ref #5

src/locales/en.json

@@ -12,5 +12,8 @@
   "city": "City",
   "location": "Location",
   "date": "date",
-  "signature": "Signature"
-}
+  "signature": "Signature",
+  "sponsoring_address_condition": "You have to provide an address if you want a donation receipt - Donation receipts can't be issued for total donation amounts under {{sponsoring_receipt_minimum_amount}}{{currency_symbol}}",
+  "sponsoring_subtitle": "On the ocation of the {{eventname}} I/We want to support",
+  "sponsoring_amount_per_distance": "with the amount of _____{{currency_symbol}} per kilometer run."
+}