891 vis walking metrics

[yf-zhou]

• Only the minimal change is included in this PR the commits are kept minimal
• Code is readable and documented in the code
• Minimal tests have been added

Add graphs to display walking metrics
navigator.py:

• call walk with parameter display_metrics=True
• visualisations are displayed at the end of the walk function
• graphs include: IMU (roll, pitch, yaw), x-y position in space, orientation and velocity, COM and footprints projected onto the same plane
• also includes functions to clear tracked data

sensors.py:

• add ability to get data from any link, not just IMU (get_pose(link_number))