Add `full_name` to `get_connection_value()`

[eriktaubeneck]

In reference to this comment, I suggest including a full_name attribute to the dictionary returned from get_connection_values() in each of the providers/provider.py.

For Facebook, it would look like:

display_name = profile.get('username', None)
full_name = profile['name']

This shouldn't break the API, unless someone is using display_name assuming it never falls back to profile['name']. This is more explicit, and should encourage people to use provider_user_id rather than display_name for any url building or other API access.

For Twitter, it would look like:

display_name = '@%s' % user.screen_name,
full_name = user.name

If there is support for this change, I will submit a pull request.

[eriktaubeneck]

Merged with pull request 20.