PublishData as object

Following the discussion in https://github.com/Azure/azure-sdk-for-python/issues/195, here is my pull request to get Publish Data as an object.
`WebsiteManagementService` has now the method `get_publish_profile` which return the publish profile as a Python object.

Since the XML format of that profile is far from usual, I had to make some adds in the reflective parsing API.
Example of object meta-definition:
```python
class PublishData(WindowsAzureData):
    _xml_name = 'publishData'
    
    def __init__(self):
        self.profile_name = _xml_attribute('profileName')
```
is a meta-declaration to parse XML as
```xml
<publishData profileName="Me"/>
```

Exactly:
- `_xml_name` will be used instead of `type.__name__` to catch the root tag
- `_xml_attribute` stands for attribute extraction instead of text node extraction