Added support for animated emoji (#913)

* Added support for animated emoji

This was such a useful feature Discord, I'm glad you added this instead
of fixing bugs.

* Fix bugs in emote parser

* Added unit tests for emotes

src/Discord.Net.Rest/API/Common/Emoji.cs

@@ -9,6 +9,8 @@ namespace Discord.API
         public ulong? Id { get; set; }
         [JsonProperty("name")]
         public string Name { get; set; }
+        [JsonProperty("animated")]
+        public bool? Animated { get; set; }
         [JsonProperty("roles")]
         public ulong[] Roles { get; set; }
         [JsonProperty("require_colons")]