Adds an icon-only version of the TabPageIndicator

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/938732/73108/8488d45e-6030-11e2-91dd-a87ad845d730.png)
![device-2013-01-16-150020](https://f.cloud.github.com/assets/938732/73109/848a57f2-6030-11e2-8fb2-711d1c6b639c.png)