Added twitter pull field and formatter

Hi,

I could not get this patch to apply cleanly, so I've re-rolled it.

Note, after adding this field to a content type anding values to a node, the Twitter feed would not render until I authenticated a Twitter account using the Twitter project.

Jason.

removed dsm();

The Twitterfield module provides a formatter that utilizes Twitter Pull for output
The differences from this patch appear to be:
- this patch stores a title in combination with the username or list
- Twitterfield configures the number of tweets on the entity display mode, rather than in the field itself

Advantages of Twitterfield
- Limit the types values being stored in the field (e.g. usernames only)
- Ability to render as just a link in other display modes