Updated some interfaces, made time syncing methods nullable for apis not using it, added optional retry checking, removed private key from api credentials, added better support for api credentials subclasses

CryptoExchange.Net/Interfaces/ISocketClient.cs

@@ -16,12 +16,6 @@ namespace CryptoExchange.Net.Interfaces
         /// </summary>
         ClientOptions ClientOptions { get; }
 
-        /// <summary>
-        /// Set the API credentials for this client. All Api clients in this client will use the new credentials, regardless of earlier set options.
-        /// </summary>
-        /// <param name="credentials">The credentials to set</param>
-        void SetApiCredentials(ApiCredentials credentials);
-
         /// <summary>
         /// Incoming kilobytes per second of data
         /// </summary>