Integrations with Export plugins

[jesusbagpuss]

[for investigation]

The id_number field is directly referenced in a few export plugins.
Some of these may support multiple IDs from this plugin.

The RDF representations might need to be considered too - mainly in ~lib/cfg.d/ (see also: eprints/orcid_support#15).

[drn05r]

There is quite a lot of code in place to ensure the highest weighted ID gets written back to the id_number field to ensure compatibility with existing plugins. I have assumed that I have no control over the future development of other plugins so I can provide ways for them to interface with this new plugin but it is up to them to decide whether the use them.

Looking at how this plugin integrates with the core codebase (github.com/eprints/eprints3.4) better integration with standard export plugins should be relatively easy. Support for standard import plugins may be more difficult. Although EP3XML import should be supported out of the box.

[jesusbagpuss]

I was thinking that this might be a 'create readme / code examples' type solution.

I'm happy that the id_number field logic/weighting are good - but that more (reliable) info into the exports is always a good thing!