Feature/websocket sequencing (#267)

Added EnforceSequenceNumbers property on SocketApiClient to configure whether websocket message contain sequence numbers and if these should be checked to be sequential
Added fallback to existing websocket connection if no dedicated request connection was found
Added IntBoolConverter base class for arbitrary int value to bool mapping
Added SequenceNumber property to DataEvent object
Added _skipSequenceCheckFirstUpdateAfterSnapshotSet property for SymbolOrderBook implementations
Updated SymbolOrderBook sequenceNumber validation
Updated SymbolOrderBook log verbosities
Renamed SetInitialOrderBook to SetSnapshot in SymbolOrderBook
Renamed updateId references to sequenceNumber in SymbolOrderBook

CryptoExchange.Net/Objects/Sockets/DataEvent.cs

@@ -53,6 +53,11 @@ namespace CryptoExchange.Net.Objects.Sockets
         /// </summary>
         public SocketUpdateType? UpdateType { get; set; }
 
+        /// <summary>
+        /// Sequence number of the update
+        /// </summary>
+        public long? SequenceNumber { get; set; }
+
         /// <summary>
         /// ctor
         /// </summary>
@@ -126,6 +131,15 @@ namespace CryptoExchange.Net.Objects.Sockets
             return this;
         }
 
+        /// <summary>
+        /// Specify the sequence number of the update
+        /// </summary>
+        public DataEvent<T> WithSequenceNumber(long? sequenceNumber)
+        {
+            SequenceNumber = sequenceNumber;
+            return this;
+        }
+
         /// <summary>
         /// Specify the data timestamp
         /// </summary>