Disruptive changes in Melodic

[j-rivero]

Here is the list of disruptive changes to be commited into Melodic that could require user reaction. Sorry for not doing them before the final release but I think it is a good time to made them:

Joint Pose Trajectory

• Remove the gazebo_ros_joint_pose_trajectory item (pr Remove deprecated plugins in Melodic #708)

Gazebo ROS Control

• Remove legacy option from gazebo_ros_control in order not to ignore robotNamespace (pr Don't ignore robotNamespace #637, pr Remove legacy in gazebo_ros_control for robotNamespace #709)

Diff Drive plugin

• Change encoder mode to send velocity from odom frame to base_link frame (#issue gazebo_ros_diff_drive in encoder mode sends velocity in odom frame not base_link frame #717, pr DIFF DRIVE: wheel odometry twist is child frame #719)
• Remove legacy protection about the inversion of right and left wheels in code (pr End of legacy for diff drive plugin #707)

Spawn Model

• Remove -gazebo option from spawnmodel (deprecated in ROS Hydro) (issue Spawn Model refactors #729)

[kev-the-dev]

Recommend adding

• remove -gazebo option from spawnmodel (deprecated in ROS Hydro), issue Spawn Model refactors #729

[davetcoleman]

Thanks @j-rivero for taking care of these migration changes, very important!

[kev-the-dev]

All items are now merged in melodic.