Added support for android:label attribute in application and activity elements

In a normal Android application, the `android:label` attribute can be used to set the title used for activities. However this attribute wasn't being parsed. Additionally, `ShadowActivity`'s methods `getTitle()` and `setTitle(String) ` implementations are not required.

Added setting of an activity's title based on the activity's `android:label` attribute if it has one, or the application's `android:label` attribute if it has one. If neither are present, then the title will be set to null.

Also added support for short class names, i.e. starting with '.' to represent that the name starts with the package name set by the manifest element's `package` attribute.