Publish Encoder data as an Odom message

[Oluwatoni]

Change the encoder message to an odom message to enable it to be fused with the imu

Acceptance Criteria
Inputs

• current steering
• current velocity

Outputs

• odom message with x, y, theta and the odometry estimate of the current position
  -base_link to odom transform

use the bicycle model for the vehicle dynamics

[Oluwatoni]

Here's a guide on how to fill out the Odom message
http://wiki.ros.org/navigation/Tutorials/RobotSetup/Odom