Sitemap tests added

As we lack tests for our code some tests for sitemap generator were implemented.
The dom parser in `minidom` as well as `ElementTree` library will count carriage returns as Dom Elements if we don't include this code. If I run the test w/o this line of code, the parsed content will be like: 
```bash
[<DOM Text node "'\n    '">, <DOM Element: url at 0x7f93e76765a0>, <DOM Text node "'\n  \n    '">, <DOM Element: url at 0x7f93e7676768>, <DOM Text node "'\n  '">]
```
This looks like this because we have carriage return after `<urlset>` tag, and after each `<url>` tag. 
I can delete this code and modify the code for dict creation in  `_get_sitemap_dict` method, but thought this would be better.