web/application: instantiate the repository outside of CubicWebPublisher This improves decoupling and allows ``CubicWebPublisher`` user to choose which argument are used during ``Repository`` instantiation. In particular is allows caller to provide a ``TaskManager``. The `vreg` argument of publisher is made mandatory. See CubicWebPublisher docstring for details. Related to #2249513

remove vreg argument to CWPublisher The passing a vreg to CWPublisher was used by test to allow reused of an existing vreg. We dropped this feature two commit ago and can safely removes it. Removing this argument allows later cleanup and improvement on the CWPublisher and Repository front. closes #2944813