Add stats plugin to registry (#296)

I have worked on stats plugin for a while now, and i have finally finished it (partly) i added paginators to it and therefor i think it can be good in the registry.

Author: KarateWumpus

plugins/registry.json

@@ -160,5 +160,14 @@
         "title": "Colors!!",
         "icon_url": "https://cdn1.iconfinder.com/data/icons/weather-19/32/rainbow-512.png",
         "thumbnail_url": "https://i.imgur.com/fSxnc9W.jpg"
+   },
+    "stats": {
+        "repository": "MiTonder/modmail-plugins",
+        "branch": "master",
+        "description": "Get useful stats directly in an embed about either the ModMail bot, a user or the server.",
+        "bot_version": "2.24.1",
+        "title": "Get Stats",
+        "icon_url": "https://image.flaticon.com/icons/png/512/117/117761.png",
+        "thumbnail_url": "http://www.pngmart.com/files/7/Statistics-PNG-Clipart.png"
     }
 }