Attempts to resolve #961 (#962)

* Move REST requests to appropiate class

* Add call to ClientHelper and expose to public API

* Expose shard count request in public api

* Expose method from interface

* Update sharded client to utilize the new method

* Method is already implemented in a base class

* Refactor name to fit pattern for methods returning a `Task`

* Adds missing ConfigureAwait

* Corrects unnecessary whitespace

* Removes unneeded whitespace

src/Discord.Net.WebSocket/BaseSocketClient.cs

@@ -1,4 +1,4 @@
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.IO;
 using System.Threading.Tasks;
 using Discord.API;