rankings: make sorting stable

[NeKzor]

Tried to optimize a few things but then noticed that the sorting is unstable which makes it hard to detect if the result is the same as before. Sorting by Steam ID on equal scores should make it stable since that field is always unique.

Example diff for sp.json where sp_score score is the same but higher Steam ID gets sorted to the back:

-  {
-    "user_name": "MrCatMcFly",
-    "avatar_link": "https://avatars.steamstatic.com/6f89591012f8f0f34cef1ecdb1c10793b0ea4bd1_full.jpg",
-    "steam_id": "76561198168920589",
-    "sp_score": 87,
-    "mp_score": 66,
-    "overall_score": 153,
-    "sp_rank": 15,
-    "mp_rank": 109,
-    "overall_rank": 28
-  },
   {
     "user_name": "BiSaXa",
     "avatar_link": "https://avatars.steamstatic.com/90864fe6d618dfeb65e0a336ae20dd949e916242_full.jpg",
@@ -175,6 +164,17 @@
     "mp_rank": 6,
     "overall_rank": 8
   },
+  {
+    "user_name": "MrCatMcFly",
+    "avatar_link": "https://avatars.steamstatic.com/6f89591012f8f0f34cef1ecdb1c10793b0ea4bd1_full.jpg",
+    "steam_id": "76561198168920589",
+    "sp_score": 87,
+    "mp_score": 66,
+    "overall_score": 153,
+    "sp_rank": 15,
+    "mp_rank": 109,
+    "overall_rank": 28
+  },