Problem: data property should be a reference

[mehdisadeghi]

Solution: revert corresponding change made in #335

@ahashibon @stefanoborini I reverted a changed which was my bad.

[mehdisadeghi]

@stefanoborini @ahashibon The regenerate brings in also the FACE change (which is removed from cuba.yml)

[ahashibon]

Thanks @mehdisadeghi, looks good to me.

[stefanoborini]

Ok, now I am confused. Didn't we agree that we had to return a copy?

[stefanoborini]

Ok, this PR is doing unrelated things so I will do the following:

1. update against a new version of simphony-metadata, extracting the relevant bits.
2. if green, merge it back here.
3. merge the yapf patch I have already.

On the rest you can discuss it among yourself, and reach a conclusion.

[stefanoborini]

I merged master after PR #363 into this one. Now it should just be the "data" change.

[mehdisadeghi]

@stefanoborini This PR is desired since it provides the expected behavior.

BTW, I realized even simphony v3.0 has been inconsistent regarding data property. Some classes such as Particle treat it as reference and some others like Particles treat it as copy.