Make TrainingContainer more similar to PyironTable

[jan-janssen]

It would be great if it is possible to include a whole project and then the job internally automatically iterates over all jobs in the project with status finished and includes them in the TrainingContainer.

[pmrv]

Would be fun, but there would be more to check than the job status. Jobs would have to at least implement HasStructure, but also actually define energies and forces (e.g. Phonopy or StructureContainer are AtomisticGenericJobs but don't have those).

[pmrv]

I'm thinking to expand the HasStructure interface to allow implementations declare that they additionally define arrays in lock step with their structures ('per_chunk' arrays in FlattenedStorage speak). For TrainingStorage that would be straightforward, but any atomistic job that implements HasStructure could then also advertise whatever other quantities they have computed for each structures (commonly energy, volume, forces, stress, etc.). With this in place the TrainingContainer can then easily check whether the job passed implements HasStructure and advertises at least energies.