Gfycat integration (#8971)

* Gfycat integration

* Added gfycat api credentials to config.

config/default.json

@@ -44,6 +44,9 @@
         "WebserverMode": "gzip",
         "EnableCustomEmoji": false,
         "EnableEmojiPicker": true,
+        "EnableGifPicker": true,
+        "GfycatApiKey": "",
+        "GfycatApiSecret": "",
         "RestrictCustomEmojiCreation": "all",
         "RestrictPostDelete": "all",
         "AllowEditPost": "always",