#5 XMCDA input / output

[Olivier Cailloux]

Provide some way to output current data to an XMCDA-encoded file, and import from XMCDA. Content from the Rubis plugin can be reused and should be generalized.

At least the part with the "kernel" data should be easy to export and import. For the plugins a contribution mechanism should be implemented, which is probably more difficult.

Benefit: ability for the user to save data, share it with someone else (supposing they do not share the same database) or re-use it later. Ability for easy import of data coming from somewhere else (provided that tools exist for spreadsheet to XMCDA, e.g., such tools should appear sometime in the future, see e.g. J-MCDA).