Adb shell input roll

Implementation for #737
This is probably not the final implementation. Making a pull request to open a discussion.

The implementation works for me using selendroid-standalone.

Here's the code how to use it:

- activate something scrollable/rollable (it might be a spinner)
- call `getSelendroidDriver().getTrackBall().roll(1, 5);`

this would roll the list and select the 5th item. First 'roll' attempt might not actually roll anything depending on number of items displayed.

I am not sure about the `selendroid-server` changes. They might not have been necessary and I haven't tested them.

Any thoughts?
ok, so I'll offer the function to roll in the Driver, but internally going to delegate it to the TrackBall class.