Sample packages on how to extend iiwa_stack.

This packages are used within the wiki of iiwa_stack to explain some concepts of its usage.
iiwa_stack needs to be present on the system to make these packages work.

In brief, here is contained :

• iiwa_tool: packages that show an example of how to add a tool to the KUKA LBR IIWA description.
• two_iiwa : packages that show an example of how to work with two iiwas (in Gazebo).