Don't put the date in Annotation#lastModifier field

Context

Since the beginning we're setting the current date to lastModfier field in order to display it on annotation tab.

This behavior leverages the code below on ARender side:

getView().setContentHeader(displayName, annotation.getLastModifier());

Where displayName is the user name and the second parameter should be the last updated date whereas it is currently the last user updating the annotation.

Technical task

ARender will change this code because sometimes user name is displayed instead of the date. So we need to align our connector to this change coming in the next ARender release.

On our hand, we need to replace the parameter in setLastModifier calls to the user updating the annotation and set the last updated date to the date field.

As we're serializing ARender annotations to String in order to store them in Nuxeo, we need to handle the backward compatibility of former annotations.