Sitemap tests added

As we lack tests for our code some tests for sitemap generator were implemented.
I'd like to save a common lambda under some variable:

```python
    def _get_sitemap_dict(self, xml):
        """
        Generates and returns python dict from an xml string passed as input.
        """
        is_element = lambda n: n.nodeType == n.ELEMENT_NODE

        root = minidom.parseString(xml).documentElement
        content = {root.nodeName: []}

        for url in filter(is_element, root.childNodes):
            url_data = {
                c.nodeName: c.firstChild.nodeValue
                for c in url.childNodes if is_element(c) }
            content[root.nodeName].append({url.nodeName: url_data})

        return content
```