Migrate to JSON i18n

Procedure per https://www.mediawiki.org/wiki/Manual:GenerateJsonI18n.php
with shim.

Change-Id: Ied3a4c392cf2ea16c6e858a1baaf9790db95e1f4

i18n/sr-el.json

@@ -0,0 +1,14 @@
+{
+    "@metadata": {
+        "authors": [
+            "Michaello",
+            "Milicevic01"
+        ]
+    },
+    "contributionscores-top": "(prvih $1)",
+    "contributionscores-days": "{{PLURAL:$1|Poslednjeg dana|Poslednjih $1 dana}}",
+    "contributionscores-allrevisions": "Svih vremena",
+    "contributionscores-pages": "Stranice",
+    "contributionscores-changes": "Izmene",
+    "contributionscores-username": "Korisničko ime"
+}