Added syntax highlighting for XML Tools (#156)

Syntax highlight now should work on all tools apart from Mock Services.

Co-authored-by: Adam Bem <adam.bem@zoho.eu>
Reviewed-on: #156
Reviewed-by: Mikolaj Widla <widlam@noreply.example.com>

Frontend/assets/css/tools/r11form.css

@@ -505,6 +505,10 @@ h2 {
     font-weight: 300;
 }
 
+pre {
+    margin: 0px;
+}
+
 @media only screen and (max-width: 1024px) {
     .rwd-hideable {
         display: none;