Adding simulation of 2 turtlebots in Comp Lab C including short tutorial

[cdondrup]

This PR includes a lot of different things for a working simulation:

• Tutorials:
  • describing how to run the standard simulator environments with an empty world
  • describing how to run the multi robot Comp Lab C world
• Adding a simulator environment that remotely looks like Comp Lab C
  • Had to add a lot of artificial structure to allow navigation and mapping
  • To support multiple robots in the same environment, the kobuki node and descriptions had to be altered.
  • Some of the turtlebot urdf files had to be altered to include the correct kobuki descriptions
  • This also meant to include the meshes as they are expected to be in the same packages as the urdf files
  • Launch files and kobuki node are mostly taken from the winter school set-up but have been altered to allow the installation an the use of the standard examples once it is installed.

The tutorials state installation instructions, listing the packages they are needed. These are also run_depends which makes this kind of obsolete. Left in there for the sake of completion.

[cdondrup]

@marc-hanheide maybe you can check if it works for you as well.