adding explicit classes for repl mode

[tlienart]

closes #1048

adds classes

• julia-repl,
• julia-repl-shell
• julia-repl-help
• julia-repl-pkg

so that

```>
x = 5
```

becomes

<pre><code class="language-julia-repl julia-repl">julia> x &#61; 5
5
</code></pre>

making it easier to be more specific and have dedicated styling or annotation for repl blocks.