Add trajectory utilities for ik, fk, pose interpolation

Extend trajectory for pose interpolation and ik/fk trajectories (i.e. mapping a trajectory of poses to (connected) joint angles and vice versa)

These can then be used e.g. for tracking a desired eef trajectory; also in combination with kunz trajectory for example:

trackable_traj = from_kunz_trajectory(ik_sols.q, 0.001, assembly.robot.joint_velocity_limits, np.minimum(assembly.robot.joint_acceleration_limits, 2.))
assembly.robot.update_configuration(trackable_traj.q[0])
vis = assembly.robot.visualize()
trackable_traj.visualize(vis, assembly=assembly)
trackable_traj.plot()