Implement 'Modify Guild Channel Positions' (#1198)

* Adding shuffleArray method to utils

* Shuffle channels functionality on guild.

* Comment fix

* Removing shuffle functionality and replacing with a simple update

* Code review changes to method/variable names

* Update comment reference to channelId as well

* Updating jsdoc with typedef of ChannelPosition

src/client/rest/RESTMethods.js

@@ -751,6 +751,15 @@ class RESTMethods {
       .then(() => user);
   }
 
+  updateChannelPositions(guildID, channels) {
+    return this.rest.makeRequest('patch', Constants.Endpoints.guildChannels(guildID), true, channels).then(() =>
+      this.client.actions.GuildChannelsPositionUpdate.handle({
+        guild_id: guildID,
+        channels,
+      }).guild
+    );
+  }
+
   setRolePositions(guildID, roles) {
     return this.rest.makeRequest('patch', Constants.Endpoints.guildRoles(guildID), true, roles).then(() =>
       this.client.actions.GuildRolesPositionUpdate.handle({