Completion of mandatory user stories

- User can sign in to Twitter using OAuth login
- User can view the tweets from their home timeline
        - displaying username, name and body for each tweet
        - display relative timestamp for each tweet
        - view more tweets with infinite pagination
        - links in tweets are clickable and will launch in a web browser
- User can compose a new tweet
        - user can click a Compose icon in the Action Bar
        - User can enter a new tweet and post this to twitter
        - User is taken back to home timeline with new tweet visible in
          timeline.
        - User can seea counter with total number of characters left for
          tweet.
- Improved app theme to feel "tweet branded"
Advanced user stories

* [x] Optional: Advanced: User can refresh tweets timeline by pulling down to refresh.
* [x] Optional: User can tap a tweet to display a "detailed" view of that tweet.
* [x] Optional: User can select "reply" from detail view to respond to a tweet.
* [x] Optional: User can open the twitter app offline and see last loaded tweets.
        - offline support is buggy. Need to debug this.
* [x] Optional: Some tweaking of colors and icons.