Improve robot body motion for balance for 8 phase gait

[mike4192]

Improve the body shift motions that occur with the 8 phase gait. Currently these motions are discreet movements which occur in between leg swing cycles (so they occur when all four legs are on the ground).

For example, the sequence is something like

1. All four legs touching ground, move body back and to the left
2. Swing front right leg
3. All four legs touching ground, move body to the right
4. Swing front left leg
5. All four legs touching ground, move body forward and to the left
6. Swing back right leg
7. All four legs touching ground, move body to the right
8. Swing back left leg
9. Back to 1....

The body shifting can probably be implemented as a smooth motion that occurs continuously during walking. This would probably smooth walking motion overall and allow faster walking speeds to be attained for this gait. A solution would potentially reduce the gait to 4 phases, with body motion being handled separately.