C# code generator improvements (#933)

* Escape quotes in generated C# strings

* Handle response with JSON body in C# code generator

test/WireMock.Net.Tests/WireMockAdminApiTests.IWireMockAdminApi_GetMappingsCode.verified.txt

@@ -16,11 +16,13 @@ server
         .UsingMethod("POST")
         .WithPath("/foo2")
         .WithParam("p2", "abc")
+        .WithHeader("h1", "W/\"234f2q3r\"", true)
     )
     .WithGuid("1b731398-4a5b-457f-a6e3-d65e541c428f")
     .RespondWith(Response.Create()
         .WithStatusCode("201")
         .WithHeader("hk", "hv")
+        .WithHeader("ETag", "W/\"168d8e\"")
         .WithBody("2")
     );
 
@@ -32,5 +34,32 @@ server
     .WithGuid("f74fd144-df53-404f-8e35-da22a640bd5f")
     .RespondWith(Response.Create()
         .WithStatusCode(208)
+        .WithBodyAsJson(new
+        {
+            a = 1,
+            b = 1.2,
+            d = true,
+            e = false,
+            f = new [] { 1, 2, 3, 4 },
+            g = new
+            {
+                z1 = 1,
+                z2 = 2,
+                z3 = new [] { "a", "b", "c" },
+                z4 = new []
+                {
+                    new
+                    {
+                        a = 1,
+                        b = 2
+                    },
+                    new
+                    {
+                        a = 2,
+                        b = 3
+                    }
+                }
+            }
+        })
     );