Add benchmarks

[felixvd]

As discussed in maintainer meetings in the past, and as demonstrated in this thread, performance benchmarks would be very useful to compare the impact of changes we consider integrating into MoveIt. Good benchmarks let developers estimate how calculation speed and precision are affected in different situations. Here is an example.

Potential benchmarks could be:

• "Simple" calls to IK
• Motion planning through scenes of differing complexity (e.g. tight spaces, many objects) using different planners
• Constructing a planning scene
• Updating collision objects in the planning scene (e.g. an octomap from one or multiple sensors)
• More realistic applications (e.g. pick-place tasks, or the MoveIt Task constructor demos)

A simple benchmark can be a good MoveIt Day project.

Related reading: 1, 2