GPII-247: Provide start and stop capabilities to Android

This pull request provides us the capabilities of start and stop applications, and can be tested by following the tutorial http://wiki.gpii.net/index.php/GPII_Android_Shared_Preferences_Example 

Also, we're adding a goToHomeScreen method in order to force the system to leave the current application and go to the home screen.

Cheers,
Javi