New sample app with a composite sensor

[brice-morin]

Provide another client app (in addition to battery logger), which demonstrates how to log composite sensors, such as the accelerometer (with x,y and z axes).

[brice-morin]

When we have this new client app, it would then be good to provide a generic client, which can introspect (at runtime) what are the sensors available on the phone/tablets: See http://developer.android.com/guide/topics/sensors/sensors_overview.html#sensors-identify