Restructure trajectory class to support leaner Cartesian/Joint trajectory types

[bpapaspyros]

We currently have an unused (but not outdated) Trajectory class:

https://github.com/aica-technology/control-libraries/blob/59e515c3d9984974cdacd4b1b86623fe80638b8a/source/state_representation/include/state_representation/trajectories/Trajectory.hpp

We could restructure it accordingly so as to support:

• CartesianTrajectory
• JointTrajectory

Then, the existing Trajectory class could be cleaned up to not require joint_names_ or a State queue but leaner data types and specialized (potentially) name vectors depending on whether we are dealing with Cartesian or Joint trajectories.

Tasks

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1. Split Trajectory class into TrajectoryBase, CartesianTrajectory, and JointTrajectory #216
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2. Update unit tests for new Trajectory classes #217
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3. Implement python bindings for new Trajectory classes #219
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4. Update/rewrite serialization of new Trajectory types

[bpapaspyros]

@domire8 I turned this into an epic and started added some tasks, feel free to give feedback and/or add items. The first item is a big one, let's discuss structure ideas in the corresponding issue (#216).