Add uses-sdk to AndroidManifest.xml

Currently the sample looks like this on a Nexus 4:
![screenshot_2013-06-19-06-39-53](https://f.cloud.github.com/assets/1798519/672999/d04ae526-d8a3-11e2-87df-a6c1ee884d7c.png)

The app is ignoring screen density. Adding a uses-sdk to AndroidManifest.xml makes it take into account screen density (and use the device default theme):
![screenshot_2013-06-19-06-40-55](https://f.cloud.github.com/assets/1798519/673003/d55327fe-d8a3-11e2-9955-d8dfcc7cd98b.png)