Set fixed link for urdf visualization marker

Set fixed link and offset for humanoid.
These are used in order to set foot on ground.
related to #115
![screenshot_from_2014-10-23 10 21 46](https://cloud.githubusercontent.com/assets/4415085/4746970/3d056f56-5a53-11e4-837b-c7c5970a037c.png)