Fix update to current geonode

This pull request updates geonode-project to work with the current version of geonode. It fixes several problems:

* incorrect naming of the PRINT_NG_ENABLED setting
* the `urls.py` was referencing a `geonode.views.index`, which does not exist (anymore). I replaced it with the definition present in the `urls.py` of geonode, which uses the `TemplateView` class to render the `site_index.html` template
* the `site_index.html` template was calling non-existent blocks. I replaced it with a copy of the `templates/index.html` file from geonode