Fix footstep frames

The translation layer used to convert footstep sole poses to origin poses was incorrect (so far this was only affecting DRC, not any of the Drake examples). I've fixed it now. 

I also updated to a better fixed point for Atlas (the same one we use in DRC) which keeps the knees a bit more bent and prevents them from going singular during walking. 
fyi - you shouldn't have to do this.  you can call forward/inverse kinematics with the frame_id and it will do all the transforms for you (often in C) and hopefully without bugs.