Added hexabot (another kind of hexapod robot for Kyoto Uni's experiments)

Hi Georg,

Here is an updated version of lpzrobots that I have added three files (hexabot robot) that Yuichi, a PhD student from Kyoto Uni who works with us, created for his robot experiments.

By the way, I just found that there is an error at

"ode_robots/simulations/nimm2_arena$ "

Error> 
start: robots/oderobot.cpp:80: virtual int lpzrobots::OdeRobot::getSensorNumber(): Assertion `initialized' failed.
Aborted (core dumped)

You make check this as well : )