Code markdown isn't preserved in card comments

[daryl-o]

If you create a code block (like XML) in the comments section of a card, the preview looks fine but the < and > tags are converted to < and > when the comment is saved.

For example

```xml
<foo> here is some XML code </foo>
```

[sridhar391]

@daryl-o if the users added any script tag content like "<script>alert(0);</script>" , we strip the tags to prevent the execution and if the user adds " here is some XML code " , it strips the tags