Request and use full_text (tweet_mode=expanded)

The module is currently getting truncated text when the Tweet is over the old 140 character limit. This patch will allow the module to request the full 280 character Tweet by using the API's tweet_mode=expanded argument.

Assuming the API returns the expanded tweet, the value is stored in $tweet->full_text instead of $tweet->text. The expanded tweet is still stored in the 'tweet_text' property of the twitter_entity.