Footstep offset to marker

support offset parameter for footstep_marker
* read `~lfoot_offset` and `~rfoot_offset`
* add .gitignore to ignore several directories created by rosbuild

In the case of HRP2JSKNT, it should be:
```yaml
      lfoot_frame_id: LLEG_LINK5
      rfoot_frame_id: RLEG_LINK5
      lfoot_offset: [0.035589, 0.01, -0.105, 0, 0, 0, 1]
      rfoot_offset: [0.035589, -0.01, -0.105, 0, 0, 0, 1]
```