Implemented the importation of photo annotations in XML, including:
- Implementing the view, with error reporting and instructions.
- Strict XML document validation.
- Schema based validation.
- Database integration.
- NYI:
-- Automatic generation of the schema file (and offering it in the view).
-- Validating the coherence between entity types and property types.
Added the nokogiri gem for XML processing.
Changed the image entity selection on the Entity Show view to have the same style as a selected entity does in the Photo Show view.
Disabled absolute paths in the configuration (should not be needed anymore, because we're using Unicorn now [tested]).