Requests for comment/Image information

We need a facility to access information from file description pages in a machine-readable format. Bits of information needed are:
 * License information
 * Image description, in user's preferred language is possible
 * Author information
 * Date image was produced
 * Source of the image
 * etc

Commons already has a rich metadata system for this - we should use it. Artworks also have a very rich set of metadata, which should be exposed as well.

Storage: page_props vs. dedicated table

 * Some fields (e.g. license information HTML) can be quite large - is it desireable to store them in page_props?
 * Some information (e.g. descriptions) might come in several languages. Storage options include: page_props with property names like 'description:de' and querying it a-la LIKE 'description:%'; or having a dedicated column for language in a separtate table?

Query requirements
In the long term it would be nice to be able to do general queries, like "give me all the images with CC-BY-compatible license that are photographs from 1970 to present within this geo box". In the short term we do not need this. :)

In the short term, we need to be able to request the data for a specific file by name. We should also be able to ask for specific set of properties only - 'get me property X, Y, Z for item File:ABC.jpeg', rather than only 'get me all properties of item File:ABC.jpeg'.