Don't use services in EntityContent

Content objects should ideally be value objects. This moves
any code that relies on services into the associated ContentHandler,
instead of having it in the Content object itself. This allows
such services to be injected when constructing the handler.

Note: getEntityView still needs to be factored out, see bug 66486.

Change-Id: I99753f806fa37bd21cc122a68dd47c4565484b25