Data Fragment Selectors using the Web Annotation Model

[floWetzels]

As already discussed in Issue #21, data fragment selectors could be modelled more precisely in json (than currently) using terms from the Web Annotation Model.

However, one main goal of this profile was to use as little external vocabulary as possible and stick to schema.org terms. Therefore, I suggest to only use the specification of data fragment selectors from there, not the acutal json model.

What do you think, @HLWeil @stuzart @muehlhaus?