Add Ur16e support (rebased on-top of melodic-devel-staging)

[gavanderhoorn]

This is @fmauch's work but rebased on-top of melodic-devel-staging.

Replaces #477. Original PR description:

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This PR aims at adding ur16e support to univeral_robot.

This basically implements #460 and UniversalRobots/Universal_Robots_ROS_Driver#73.

It is built upon #371 and #414 so it will have parametrized xacro files and support for robot calibration.

The current status:

• Add config files for ur16e
• Add description launch files for ur16e
• Add gazebo launchfile for ur16e
• Add meshes of upper and lower arm. To my knowledge all other segments are the same as for the ur10e. The arm segments are also the same, but shortened. So, taking out a part in the middle should be sufficient.
• Update physical and visual parameters. I started working on those, but many of them are copied from the ur10e
• Add ur_kinematics files for the ur16e
• Add ur16_e_moveit_config

[gavanderhoorn]

Git never ceases to surprise me: I had quite a convoluted local history with missing commits etc, but it was still able to rebase #477 on-top of melodic-devel-staging without me having to do anything manually. 👍

[gavanderhoorn]

We'll merge this without the additions to ur_kinematics, nor include a MoveIt configuration.

We'll first get melodic-devel-staging sorted out (#448), then add the missing parts for the UR16e.

For now users could use Trac IK.

[gavanderhoorn]

As #477 was rebased, we'll merge that one instead.