Improve define-person

[didierverna]

Make define-person behave like define-sponsor, i.e. reference a person with a symbol. This would allow to reference persons by symbol instead of by names (strings) in the programme, for instance. This would also allow different persons to be created after a unique physical person (e.g. me as an administrator impersonating ELS, and me as an author, the real me).

[Shinmera]

I'm not sure about the reasoning behind this. Generally in order to uniquely identify the person, you would have to name them after their full name in the symbol again, which would just duplicate the information. Otherwise, if you choose something else for the symbol name, then figuring out who is who from cross references like in the programme would be much more difficult. I also don't understand why you would want to have multiple person entries for the same "physical person", given that conveying the relation of the person to the conference is solved through the roles list already.

[didierverna]

I don't really mind if we still use strings instead of symbols, but the problem I have is that me as the website maintainer is different from me as an author (different email address, different website etc.). So different roles may imply different person attributes which is not currently supported.

In fact, this currently matters for the pages footer only, but who knows what could be coming next. Maybe we just need a special person for the webmaster right now.

[Shinmera]

Ah- I see.

Right now I'm thinking that there might be some general value in having an inheritance-like system to solve both this, and #2. Adding inheritance to the system would allow you to define global objects and then specialise their attributes for each edition, potentially creating further copies depending on need like it is here.

I'll need some more time to think on how this should all work and fit together, though.