Fix issue with spaces after comma and or filters

Combined filters separated with comma and a space resulted in an error. 
Example: 
Title==D, (Title|LikeCount)==3
Caused the error: "(Title not found"

Extended regex to allow whitespaces after the comma as documented.

Sieve/Models/SieveModel.cs

@@ -13,7 +13,7 @@ namespace Sieve.Models
         where TFilterTerm : IFilterTerm, new()
         where TSortTerm : ISortTerm, new()
     {
-        private const string EscapedCommaPattern = @"(?<!($|[^\\])(\\\\)*?\\),";
+        private const string EscapedCommaPattern = @"(?<!($|[^\\])(\\\\)*?\\),\s*";
 
         [DataMember]
         public string Filters { get; set; }