Add per-product information to AMQP messages

This adds a more complex data structure to the AMQP messages for storing per-product information. A new products list has been added that contains the g2g_name of the G2G product and a files list of geotiff files for that product. Right now that should only be one file per product per AMQP message, but I didn't want to lose the possibility of handling multiple files in the future.