Content view register

Finaly!

Should implement #691
If making a new path available, it is best to override the `path` method. For example:

```python
def path(self, which):
    if which == 'publish':
        return '{0}/publish.format(self.path(which='this'))
    return super(...).path(which)
```

A set of unit tests can then be added in `tests/robottelo/test_entities.py`.