Fix entity-type detection when deserializing

When we don't know the java type at compilation (automation and/or adapter cases), the nuxeo response converter try to extract entity-type from response to deduce the java type to give to Jackson.

There's a bug in the regexp used to get entity-type, following json will return task instead of tasks:

{
	"entity-type": "tasks",
	"entries": [{
		"entity-type": "task",
	}]
}

Note: converter will also try to get it from header, but this doesn't fully work server side -> remove this part.