Add homing functionality

[giusebar]

Hi,

I've implemented homing functionality for the drivers.
The implementation requires the user to set up homing parameters from the configuration yaml file.
Two services are implemented that allows to start and interrupt homing procedure.
To start and stop the homing procedure two service calls have been added, namely:

• /start_robot_homing

• /stop_robot_homing

The implementation is shown in #20

Cheers,
Giuseppe