Feature bonares metadata

[mwallschlaeger]

First step on fully implementing the Bonares Metadata Schema into GeoNode. The implemantation of the Bonares MD Schema is structured into several substeps:

• Model: adopt metadata datamodel to store bonares metadata
• API: the geonode rest api, to get and set bonares metadata values
• Forms: to edit bonares metadata on the web ui
• Admin: changes to the admin interface, for example to set values which are available under certain categories
• XML: update the xml output so it follows the bonares metadata schema
• Translation: translation on the User Interface to show metadata in correct language
• UI: on the User Interface to show bonares metadata

This PR focused on the Model and API part, manipulate some of the forms and added default values for all the choosable fields coming from the bonares metadata. All this is documented inside of the bonares_metadata_mapping.xlsx file within the repository.

[mwallschlaeger]

as far as i can see this looks fine to me