Added default margins

BlackRock.Reporting.API/Core/Models/OptionsForPdf.cs

         /// <summary>
         /// Paper margins, defaults to none
         /// </summary>
-        public MarginOptions MarginOptions { get; set; } = new MarginOptions();
+        public MarginOptions MarginOptions { get; set; } = new MarginOptions(){Top="3.0 mm",Right = "3.0 mm",Left="3.0 mm",Bottom="12.7 mm"};
 
         /// <summary>
         /// Give any CSS <c>@page</c> size declared in the page priority over what is declared in <c>width</c> and <c>height</c> or <c>format</c> options.