Allow HTML in description fields, optionally

A number of data-servers permit their users to create rich HTML descriptions for products and enterprises, so that they can include image, video, and other elements.

In products and enterprises we are temporarily stripping HTML from the description fields, so that list components include only text and not (for example) videos, images and graphs.

In future we would like to render the rich HTML description in some contexts, such as the detail page of a product or enterprise.

To achieve this we should store two description fields, one with HTML-enabled content and one HTML-disabled description. In enterprise we already have long_description, but it refers to an OFN ontology. I think that we may want to achieve it by expanding on the DFC ontology.