Adds an icon-only version of the TabPageIndicator

(resubmitting on dev branch after reading comments on other pull requests)

I added the ability in TabPageIndicator to use a centered icon in the case where a null or empty title is provided by FragmentPagerAdapter and a resource id is supplied by getIconResId (from IconPagerAdapter interface). This includes a new sample Activity in the Tabs section (Tabs/Icon Only)

![device-2013-01-16-150013](https://f.cloud.github.com/assets/938732/76030/f165fd00-60de-11e2-8815-06a12dbea884.png)

![device-2013-01-16-150020](https://f.cloud.github.com/assets/938732/76031/f62dd682-60de-11e2-8dd0-30ab458d040d.png)