Create a dummy driver that supports ros_control

The empty driver implements the mechanics to report a joint position.
Later these mechanics will be moved to the JSON based driver.

Signed-off-by: Karl Damkjær Hansen <kdh@es.aau.dk>
Provide position control for empty davinci driver.

Signed-off-by: Karl Damkjær Hansen <kdh@es.aau.dk>
Major Rewrite of driver structure.

The sbrio drivers are put into their own classe that are managed
by the davinci_driver which is wrapped in the ros_davinci_driver
which is initialized in ros_driver.

Signed-off-by: Karl Damkjær Hansen <kdh@es.aau.dk>
Correct the JSON protocol

Now the driver should conform to the davinci transfer protocol.

Signed-off-by: Karl Damkjær Hansen <kdh@es.aau.dk>