Export/import of comments (#1760)

[CasperWA]

This fixes #1760.

Comments can now be exported/imported using export-version 0.4.

At this stage of the implementation, all comments pertaining to a node chosen for export will be exported.
Comments cannot be exported by themselves, nor is a Comment a valid entity to export directly, i.e. comments can only be exported indirectly through nodes.

There is a suggestion to add a flag to ex-/include comments when exporting.

If multiple users add comments to a node, all users will be exported recursively.

Examples of how data.json and metadata.json might look have been updated with Comment in the documentation.

An additional pair of joins has been added to QueryBuilder:

• with_comment to join a Comment to a User
• with_user to join a User to a Comment

These, along with a similar pair of joins for Node, has been added to the table of Joining entities in the documentation.

Lastly, Comment can now be imported directly from aiida.orm.

[coveralls]

Coverage increased (+0.01%) to 69.669% when pulling dfa7ccc on CasperWA:fix_1760_export_import_comments into a000899 on aiidateam:provenance_redesign.

[CasperWA]

Latest commit adds support for excluding export of Comments.

Using the flag include_comments=False when using export(), Comments, and any associated Users that were not already related in the export, are excluded from the export.

The same flag is added to verdi export create in the following way:
"--include-comments/--exclude-comments", "-c / -xc"

The default is to include Comments (and any associated User entities not already included through other exported entities).

[sphuber]

Some minor changes, but otherwise looks good

[sphuber]

This has gone through review and after other blocking PRs are resolved I will rebase and merge

[szoupanos]

Just modify a bit the test to make sure that you export also users that did a comment on a node that was not created by them (the user that created a node will be exported anyway).

[szoupanos]

I would not merge provenance_redesign' into your branch but rebase your branch to accommodate the changes of provenance_redesign.

[CasperWA]

I would not merge provenance_redesign' into your branch but rebase your branch to accommodate the changes of provenance_redesign.

Sure. I 'accidentally' pressed the "Update branch" button :)
But in the end it should all be squashed and rebased in any case. So I do not think it is an issue.

[sphuber]

@CasperWA In this case it still is less convenient because there are merge conflicts that I had to resolve locally. Due to the merges I couldn't simply squash your commits and then do a single rebase. Instead I had to merge it. I hope when we squash merge it will still be attributed to you, but I am not sure what will happen since the last commit is now mine, despite it being just a merge commit.

Comments have been addressed

[sphuber]

Great success, thanks a lot for the great work @CasperWA !