Make nuxeo-user-suggestion support prefixed ids

On some tasks the task actor will not be a entity-type but id:{user: jdoe} of even id:{group: member}

Reproduce

• start parallel workflow as Admin in JSF ui
• select a member user as participant / or a group
• login as that user

This results in several bugs:

1. on the task layout, in assigned to: will apper [object object] (as it is not entity-type)
2. if you navigate to the task with assigned user, the process task top bar will not appear
3. if with 'group:' prefix the task wont appear in the document view nor in the task list

Note
Getting the username tasks from Rest API should return every task of that user.