Provide facility to add new entities

[andresgruber]

During the annotation process, a human might want to add a new entity to the entity dataset, if there is no enhancement available for a given string.

It requires the following steps to creating a new entity:

1. Selecting a string
2. Search / autocomplete, if no result, then:
3. {add new} 4.a. PUT RDF/JSON --> entityhub "mark its status as proposed". 4.b. WRITE RDFa into the html

At the next use of the annotate.js, the according entity should be availbable